Mechanical Properties of 5052/2017 Dissimilar Aluminum Alloys Deposit by Friction Surfacing* 1

Transcription

1 Materials Transactions, Vol. 47, No. 3 (6) pp. 874 to 882 #6 The Japan Institute of Light Metals Mechanical Properties of 552/7 Dissimilar Aluminum Alloys Deposit by Friction Surfacing* Hiroshi Tokisue, Kazuyoshi Katoh, Toshikatsu Asahina and Toshio Usiyama ; * 2 College of Industrial Technology, Nihon University, Narashino , Japan 552 aluminum alloy plate used for substrate and 7 aluminum alloy bar used for coating rod, both monolayer and multilayer friction surfacing were done using a numerical controlled full automatic friction welding machine. Effects of the surfacing conditions on structure and mechanical properties of both monolayer and multilayer deposits were investigated. It was clearly observed that the circular pattern appeared on the surface of both monolayer and multilayer deposits by the rotation of coating rod, and the interval of circularly pattern become narrower with increasing of the rotation of coating rod. The monolayer deposit has a tendency to incline toward right side (Retreating side) further than center of deposit for the feed direction of coating rod. And, the 2nd surfacing of multilayer deposit recognized to incline toward the st deposit side. A little of incomplete welds was observed at both sides of monolayer deposit. The incomplete parts of welds st deposit in multilayer deposit were disappeared by 2nd surfacing. Microstructures of both monolayer and multilayer deposits were finer than those of the substrate and coating rod. The deposition efficiency of 2nd surfacing in multilayer deposit showed higher value than that of the monolayer deposit. Hardness of both deposits showed higher value than that of the substrate and same value of coating rod. The softened area was recognized at 2.5 mm distance from the weld interface of substrate and coating rod. The tensile strength of multilayer deposit showed higher value than that of the monolayer deposit, and both deposits showed higher value than that of the substrate. (Received August 29, 5; Accepted December 5, 5; Published March 5, 6) Keywords: friction surfacing, multilayer deposit, dissimilar coating rod, deposition efficiency, mechanical properties. Introduction Several methods of surface modification for materials by adhered the materials with the high functionality on the surfaces of plate have been tried to improve their function, and some practical achievements have been reported. ) The authors studied the effect of surfacing conditions on the shape of deposit and mechanical properties of friction surfaced material, combining 552 aluminum alloy plate and bar. 2,3) This was first report as the basic study to confirm the effectiveness of friction surfacing as a method of surface modification. Although practical application has not to been completely developed yet the formation of solid deposits can be formed using comparatively simple equipment. As the results, the thickness of deposit was able to be controlled, if the appropriate surfacing conditions were chosen, and it was clarified that good deposit was obtained. The similar friction surfaced material using 552 aluminum alloy plate and bar (hereafter called similar surfaced material) was possible to form a deposit with the fine structure on the substrate. However, the softening area has been observed in the vicinity of deposit on the substrate. Although the elongation of the surfaced material was showed higher than that of the substrate, the tensile strength of surfaced material was reduced to about 9% of the substrate. There is thus no advantage of this type of friction surfacing in terms of mechanical properties. Therefore, considering the known advantages of friction surfacing and the industrial significance of surface modification, it is necessary to use the coating materials which exhibit high hardness of the surface or enhanced strength of the surfaced material. * This Paper was Originally Published in Japanese in J. Jpn. Inst. Light Met. 54 (4) * 2 Graduate Student, Nihon University. Present address: Furukawa-Sky Aluminum Corp. Oyama , Japan According to our previous studies on some aluminum alloys used for friction welding 4 8) which is a similar technique to friction surfacing, based on the effective use of friction heat, the maximum temperature of the friction welding is slightly higher than that of the friction surfacing although its heat cycle is similar to that of the friction surfacing. For a friction welded 7 aluminum alloy joint, 4) when the joint left at room temperature after welding, the hardness of the softening area was generally improved by natural aging to a level of the base metal. This suggests that use of 7 aluminum alloy as a coating material may be able to ensure sufficient strength of friction surfaced material even if no post heat treatment is performed. From the viewpoint of save energy, it is considered that the 7 aluminum alloy is a suitable material for coating material on the friction surfacing. The other side, to realize improved functionality of the material, which is one of the purposes of friction surfacing, wider deposits are often necessary to achieve that purpose from the deposition efficiency. Although expansion of the surface area of the surfaced material can be conceived to increase the deposit area, this leads to an increase in the friction pressure required during the friction surfacing process, and therefore is not necessarily advisable in relation to the equipment. Another method that has potential is multilayer friction surfacing can be applied by repeated friction surfacing. In this study, the monolayer and multilayer dissimilar friction surfacing were conducted with 552 aluminum alloy plate as a substrate and 7 aluminum alloy bar as a coating material (hereafter called dissimilar surfaced material). Effect of surfacing conditions on the structures and mechanical properties of the friction surfaced materials was studied.

2 Mechanical Properties of 552/7 Dissimilar Aluminum Alloys Deposit by Friction Surfacing 875 Table Chemical compositions of base metals. (mass%) Materials Si Fe Cu Mn Mg Cr Zn Al 552 plate bal. 7 rod bal. Table 2 Mechanical properties of base metals. Materials Tensile strength (MPa) Elongation (%) Hardness (HV.) 552 plate rod Table 3 Friction surfacing conditions. Fig. Sampling positions of tensile test specimen. Friction pressure, P (MPa) 25, 3, 35, 4 Rotational speed, N (s ) 3.3, 6.7,., 23.3 Feed speed, f (mm/s) 5, 7, 9, Offset of 2nd layer, G (mm), 5,, 5 2. Materials and Experimental Procedure 552 P-34 aluminum alloy plate of 5 mm thickness as a substrate was machined to 5 mm width 5 mm length. 7 BE-T4 aluminum alloy bar of mm in diameter and mm length was used as a coating rod. The chemical compositions and mechanical properties of these base metals are shown in Tables and 2, respectively. The friction surfacing was conducted by restricting the length of the coating rod (i.e., the surfacing operation was terminated when 3 mm of the coating rod had been consumed), as in previous reports. 2,3) The friction surfacing was performed under the surfacing conditions shown in Table 3. However, preheating was conducted for 3 seconds at the starting position referring to the results of preliminary experiment. 2,3) Rotation of the coating rod was set to the lower speed than that used for the 552 aluminum alloy rod. As reported in the preliminary experiment, this was done because, rotational speed of coating rod over 25 s resulted in fracture of the rod and not obtained good surfaced material. Multilayer surfacing was conducted at a friction pressure of P ¼ 3 MPa with a rotational speed of the coating rod of N ¼ : s and a feed speed f ¼ 9 mms from the results of only one layer friction surfacing 2,3) (hereafter called monolayer surfacing). After the first layer had been deposited, the surfaced material was cooled down to room temperature, and then the second surfacing was conducted (hereafter called multilayer surfacing). In the multilayer surfacing process, the feed direction of the second layer deposit displaced parallel to those of the first layer deposit by the preset offset amounts shown in Table 3, either on the advancing side (i.e., in the direction in which the coating rod is shifted forward; AS) or on the retreating side (i.e., in the direction in which the coating rod is shifted backward; RS). Observation of the appearance, macro- and microstructures, hardness measurements and tensile tests of the deposit and surfaced material were conducted at the room temperature. These tests were performed on the 4th days after the friction surfacing because no further change in hardness was observed. Tensile test specimens with the same shape and size in the previous reports, 2,3) 3.5 mm in thickness, mm in width, 4 mm in length, were taken from the gauge part at the position of the surfaced material shown in Fig.. The surfaced materials were machined so that the ratio of the deposit thickness to the gauge part thickness was % for monolayer surfaced material and 4% for multilayer surfaced material. 3. Experimental Results and Discussion 3. Observations of appearance and shape of deposits The appearance of the monolayer and multilayer deposits are shown in Figs. 2 and 3, respectively. The circularly patterns made by rotation of the coating rod were clearly observed on the surface of both monolayer and multilayer deposits, regardless of the surfacing conditions. These circularly patterns are similar to those that appeared on the surface of the monolayer similar surfaced material 2,3) or friction surfaced mild steel. 9) The intervals between the circularly patterns observed on the surface of the monolayer deposits became narrower with increasing rotational speed of the coating rod and decreasing feed speed. The deposit has a tendency to incline toward the retreating side as observed in similar surfaced materials. This inclination tended to increase with increasing both friction pressure and feed speed of coating rod. The inclination of the deposit was caused by the mechanical action due to a combination of the rotational direction of coating rod and surfacing direction, and was smaller than those observed in the similar surfaced materials. 2,3) This was possibly caused by smaller deformation of the 7 aluminum alloy used as the coating rod, because its elevated-temperature strength was higher than that of 552 aluminum alloy. As for the appearance of multilayer deposit, it is not recognized the clear difference between the first and second deposits, and the second deposit did no influence on the first deposit. When an offset was given during the second surfacing, the inclination of the second deposit was not related to the direction of the offset, and in all cases the second deposit showed a tendency to incline toward the first

3 876 H. Tokisue, K. Katoh, T. Asahina and T. Usiyama Fig. 2 Appearances of monolayer deposit under conditions of friction pressure 3 MPa and feed speed 9 mms. The marks show center of coating rod. deposit. This inclination was larger when the offset was set at the advancing side and tended to decrease with increasing amount of offset. This may have occurred because the coating rod was more easily pushed out toward first deposit due to the presence of the first deposit, and the amount of coating rod pushed out decreased as the offset value increased. When the offset direction was set to the retreating side, the magnitude of offset was observed to have little influence on the inclination of deposit. In case of monolayer surfacing described above, this would be presumably due to the tendency for the deposit to incline toward the retreating side because of the relationship between the direction of rotation of coating rod and surfacing direction. Figure 4 shows the effect of the rotational speed of coating rod on the thickness, width and extension of the deposit. The thickness of the deposit decreased with increasing both feed speed and rotational speed of the coating rod, regardless of the friction pressure. Furthermore, the influence of feed speed and friction pressure became less significant with increasing rotational speed of the coating rod. The deposit showed a tendency to narrow with increasing both rotational speed of the coating rod and feed speed. Although these tendencies are similar to those observed in the similar surfaced materials, the thickness of deposit was thinner and the width of deposit expanded with an increase in the friction pressure in comparison with those of similar friction surfaced materials. It has been reported that a SS4 steel substrate is friction surfaced with a SUS43 steel coating material. According to this report, the movement of Fig. 3 Appearances of multilayer deposit under conditions of friction pressure 3 MPa, rotational speed. s and feed speed 9mms. : Center of st coating rod, : Center of 2nd coating rod.

4 Mechanical Properties of 552/7 Dissimilar Aluminum Alloys Deposit by Friction Surfacing 877 Fig. 4 Relation between rotational speed and thickness, width and length of monolayer deposit. friction interface to the axial direction, namely the thickness of deposit, increases as the rotational speed of coating rod in the surfacing becomes slower. 9) In this experiment, there was the increase of the thickness of deposit when rotational speed of coating rod was slow. The ideal length of the deposit is mm, i.e., the sum of the feed distance and the feed of the coating rod, because the feed distance of the coating rod is mechanically constrained to a maximum of 9 mm in relation to the substrate. The maximum deposit length of mm was obtained at lower friction pressure such as 25 or 3 MPa, independent of both rotational speed of coating rod and feed speed. Under the condition of high friction pressure, on the other hand, the deposit length tended to become shorter with a reduction in the rotational speed of coating rod. The deposit length became greater than that of the similar surfaced material under the same surfacing conditions. This was caused by the difference in elevated-temperature strength between 552 and 7 alloys. There was less deformation of the 7 alloy at elevated-temperatures than that of the 552 aluminum alloy, leading to a smaller transferred as a burr. It is also considered that the deposit length is shortened with increasing friction pressure, which is caused by an increase in the burr transfer of coating material, leading to an increased rate of consumption of the coating rod. Appearances of the multilayer deposits showed no clear visible difference in the deposit length between the first and second deposits. Therefore, as the shape of deposit, the thickness and width of deposit were measured. The measurement results are shown in Fig. 5. The deposits tended to a little thicker for the cases with 5 and mm offsets than Thickness / mm Width / mm RS AS Offset of 2nd layer / mm : position (a) : position (b) : position (c) Fig. 5 Relation between offset of 2nd coating rod and thickness and width of multilayer deposit. without offset, and to be slightly thinner than the 5 mm offset. The second deposit of the multilayer surfaced material became thicker and narrower than that of the monolayer surfaced material. 3.2 Deposition efficiency In friction surfacing, the entire coating rod is not consumed

5 878 H. Tokisue, K. Katoh, T. Asahina and T. Usiyama Deposition efficiency / % Friction pressure / MPa (a) N=.s -, f=9mm s Rotational speed / s - (b) P=3MPa, f=9mm s Traverse speed / mm. s - (c) P=3MPa, N=.s - Fig. 6 Effect of friction surfacing conditions on deposition efficiency of monolayer deposit. 7 Deposition efficiency / % RS AS Offset of 2nd layer / mm Fig. 8 Macrostructures of monolayer deposit under conditions of rotational speed. s and feed speed 9 mms. Fig. 7 Effect of offset of 2nd coating rod on deposition efficiency of multilayer deposit. by the deposit on the substrate, regardless of the coating material; part of the coating rod is transferred outside in addition to the burrs generated by friction welding. 4) It is not illustrated, the appearance of coating rod after surfacing though there was a difference in comparison with the case in which similar material was used for coating rod at the transferred of the burr, it was an aspect of the similarity. The deposition efficiency was determined based on the assumption that weight ratio of the coating rod before and after surfacing associated with the shape of deposit. The results of measurements of deposition efficiency of monolayer and multilayer surfaced materials are shown in Figs. 6 and 7, respectively. The deposition efficiency of monolayer surfacing was lowered with increasing both friction pressure and rotational speed of the coating rod, and especially rotational speed remarkably affected it. In addition, the deposition efficiency was slightly improved with increasing feed speed. The deposition efficiency was improved a little in comparison with similar surfaced materials 2,3) under all surfacing conditions. The difference could not be clearly recognized when the effect of surfacing conditions on deposition efficiency was compared in case of similar surfaced material. The deposition efficiency of the second deposit in multilayer surfacing was the smallest with a zero offset, i.e. when the second layer was surfaced just above the first layer. The deposition efficiency was improved with increasing offset value. The maximum deposition efficiency was obtained at an offset of 5 mm in the advancing side, and its value was approximately 53%, which was higher than that of the monolayer surfacing under the same surfacing conditions. 3.3 Observations of macro- and microstructures Figure 8 shows the macrostructures of cross section of the monolayer surfaced material. The weld interface can be clearly distinguished between the deposit and substrate. A small amount of incomplete welded part was also observed on both sides of the deposit. These defects are presumably caused by a non-effective friction pressure applied at the edges of the deposit; the deposit width was 2.3 mm, whereas the diameter of 7 aluminum alloy rod used as coating rod was only mm. Although observations of the weld penetration of coating material into a substrate have been reported in surfacing by fusion welding, ) this is because friction surfacing is a solid phase surface modification technology; no penetration of the coating material into the substrate was not observed in friction surfacing. On the other hand, the mechanically mixed

6 Mechanical Properties of 552/7 Dissimilar Aluminum Alloys Deposit by Friction Surfacing 879 Fig. 9 Macrostructures of multilayer deposit under conditions of friction pressure 3 MPa, rotational speed. s and feed speed 9mms. Fig. Microstructures of monolayer deposit under conditions of rotational speed. s and feed speed 9 mms. layer has been observed on the weld interface of dissimilar friction welded 7/552 alloys joint. 8) However, in this experiment, the mechanically mixed layer was not observed at the weld interface between the deposit and the substrate. Figure 9 shows the macrostructure of the multilayer friction surfaced material. For the multilayer friction surfaced material, both inside of the deposit and interface between deposit and substrate showed similar appearance to that of the monolayer surfaced material. At the part where the first deposit and second deposit overlap, the incomplete welded part of the deposit and substrate at the edge of the deposit observed on the first deposit had been joined by heating and compression during surfacing of the second deposit. However, some incomplete welded part was observed at both edges of the second deposit as in the case of first deposit. The microstructures of monolayer and multilayer surfaced materials are shown in Figs. and, respectively. They were observed in the center of rotational position of coating rod. The inside of the deposit had a fine lamellar structure than that of the base metals of both coating rod and substrate. Other conditions also brought about the morphology of the similarity, and the clear differences could not be recognized for structure in deposit by the difference of coating material and surfacing conditions. 3.4 Hardness distribution Figure 2 shows the hardness distribution of the monolayer surfaced material. There was a softening area at.5 mm, the nearest point from the deposit, and the hardness of the softest point was similar to that of the substrate with O- treatment. The softening area was not symmetrical with respect to the center of rotation of the coating rod, but tended to incline to the retreating side. This possibly occurred because the formation of the deposit was also inclined to the retreating side, as shown by the appearances of the deposits. The width of the softening area corresponded well to the width of the deposit. The softening area became narrower with increasing distance from the deposit, and the hardness of the softest area tended to increase with increasing distance, and the softening area were barely observed 2.5 mm away from the deposit. As shown in the hardness distribution of the cross section, the hardness of deposit was harder than the substrate. The hardness of the deposit approaches the surface layer, and hardness of the surface layer was approximately 3 HK, which is equivalent to that of the coating material. The hardness distribution of the multilayer surfaced material is shown in Fig. 3. The measurements were conducted 4 days after friction surfacing. A softening area corresponding to the deposit width was observed in the

7 88 H. Tokisue, K. Katoh, T. Asahina and T. Usiyama Fig. Microstructures of multilayer deposit under conditions of friction pressure 3 MPa, rotational speed. s and feed speed 9mms. substrate, as was the case in the monolayer surfaced materials. In case of the zero offset, the hardness of the softest area in the substrate was a little lower in comparison with that of the monolayer surfaced materials. When an offset was given, the hardness of softening area was similar to that of the monolayer surfaced materials. The hardness distributions on the cross section of the multilayer surfaced material showed a similar tendency to that of the monolayer surfaced material, regardless of the offset. In case of coating rod without offset, the hardness value of the deposits of both the first and second deposits were higher than that of the substrate, and were equivalent to that of the coating material. For the coating rod with some offset, the hardness inside the first deposit increased with increasing distance to the second deposit, and the entire cross section of the second deposit had a hardness equivalent to that of the coating material. This difference in hardness within the first deposit was presumably caused by variability in the effect of heat on the first deposit during the second layer surfacing. The hardness at the middle points between the center of rotation of coating rod in the first and second deposits showed values corresponding to the magnitude of offset, because the effect of heat decreased with increasing offset. 3.5 Tensile tests Results of the tensile tests of the monolayer and multilayer surfaced materials are shown in Figs. 4 and 5, respectively. The tensile strength of the monolayer surfaced material increased with increasing both friction pressure and deposit thickness, and decreased with increasing feed speed. In this experiment, the highest tensile strength of 267 MPa was obtained at a friction pressure of 4 MPa. This value was higher than that of the 552 aluminum alloy used as a substrate. Elongation showed a tendency to increase with increasing friction pressure and decrease with increasing feed speed. However, the influence of rotational speed of the coating rod on elongation was minimal. The degree of elongation of the surfaced material was less than that of the substrate under all the surfacing conditions. This is probably due to the difficulty in achieving uniform deformation in the surfaced material specimens whose parts are deposits. Although, with the 552 aluminum alloy substrate, higher tensile strength was obtained in the multilayer surfaced

8 Mechanical Properties of 552/7 Dissimilar Aluminum Alloys Deposit by Friction Surfacing RS 9 AS Hardness / HV. Hardness / HV Distance from the interface 5.5mm.5mm 2.5mm 4 Distance from center / mm (a) Matrix AS G= G=RS5 G=AS5 5 Distance from center / mm (a) Matrix Deposit Matrix Deposit 8 4 Hardness / HK. Hardness / HK. RS G= G=RS5 G=AS Distance from the interface / mm (b) Cross section 5 Fig. 2 Hardness distributions of monolayer deposit under condition of friction pressure 3 MPa, rotational speed. s and feed speed 9 mm s. Matrix Distance form the interface / mm 3 (b) Cross section Fig. 3 Hardness distributions of multilayer deposit under condition of friction pressure 3 MPa, rotational speed. s and feed speed 9 mm s. Fig. 4 Results of tensile test of monolayer deposits. material than that of the monolayer surfaced material, the difference in tensile strengths caused by differences in the magnitude of the offset was small enough for tensile strength to be considered virtually constant. In case of the zero offset, the elongations were equivalent to those of the monolayer surfaced materials which had the smallest elongation, and the ones with the offset given showed a tendency of lower elongation with a bigger offset, regardless of the direction of the offset. If the strength of the surfaced material is assumed to simply follow the rule of mixture, the tensile strength of the surfaced material should be 288 MPa for monolayer surfaced

9 882 H. Tokisue, K. Katoh, T. Asahina and T. Usiyama Fig. 5 materials and be 39 MPa for multilayer surfaced material. The maximum tensile strength of monolayer surfaced material was 9.4% of this value and that of multilayer surfaced material was 95.2%, indicating that the rate of increase in tensile strength was improved by multilayer surfacing. Observation of the near the fractured position showed a small exfoliation at the interface between the deposit and substrate in a monolayer surfaced material processed at low pressure of 25 MPa. In other specimens, the exfoliating in the interface could not be recognized. 4. Conclusions Results of tensile test of multilayer deposits. The monolayer and multilayer friction surfacing were conduced using 7 aluminum alloy rod as a coating material which is higher strength than the 552 aluminum alloy used as a substrate. The influence of the surfacing conditions on the structures and mechanical properties of the surfaced material has been investigated. The following results were obtained. () The circularly patterns generated by the rotation of the coating rod were clearly observed on the deposit surfaces of both monolayer and multilayer surfaced materials. The deposit tended to incline to the retreating side in the monolayer surfacing, and the second deposit in the multilayer surfacing tended to incline to the first deposit regardless of the offset direction. (2) From the observation of macrostructures, it was observed incomplete welded part at either edge of the interface between the deposit and substrate in the monolayer surfaced material, whereas in the multilayer surfaced material the portion of the first deposit overlapping with the deposit of second layer surfacing was firmly welded. The inside of the deposit had fine lamellar structures than those of the coating material and substrate. (3) The deposition efficiency of the multilayer surfacing was higher than that of the monolayer surfacing. (4) The hardness of the deposits in the both monolayer and multilayer surfaced materials were equivalent to that of the coating material. A softening area was observed in the substrate immediately below the deposit. This softening area became narrower with increasing distance from the surfaced interface between deposit and substrate, and it disappeared at 2.5 mm from the surfaced interface. (5) The tensile strength of the monolayer surfaced material was higher than that of the 552 aluminum alloy used as the substrate. Further, it increased with increasing both friction pressure and rotational speed of coating rod, and decreased with increasing feed speed. In multilayer surfaced materials, effect of the offset on the tensile strength could be hardly recognized. The tensile strength of multilayer surfaced material was higher than that of the monolayer surfaced material. Acknowledgements This research is supported by both the Grant-in-Aid for Scientific Research (c) (grant No. 4557) and the Technology to Special Research Grants for the Development of Characteristic Education from the Ministry of Education, Culture, Sport, Science and Technology. Authors wish to express our sense of gratitude by making special mention here. REFERENCES ) For example, E. D. Nicholas and W. M. Thomas: Weld. J. 65 (986) ) H. Sakiyama, H. Tokisue and K. Katoh: Mater. Trans. 44 (3) ) H. Sakiyama, H. Tokisue and K. Katoh: J. Jpn. Inst. Light Met. 52 (2) ) H. Tokisue and K. Katoh: J. Jpn. Inst. Light Met. 28 (978) ) K. Katoh and H. Tokisue: J. Jpn. Inst. Light Met. 4 (99) ) K. Katoh and H. Tokisue: J. Light Met. Weld. Construction 32 (994) ) K. Katoh and H. Tokisue: J. Jpn. Inst. Light Met. 48 (998) ) H. Fuwano, K. Katoh and H. Tokisue: J. Jpn. Inst. Light Met. 5 () ) K. Fukakusa: J. Jpn. Friction Weld. Association 2 (995) ) For example, Y. Kanbe et al.: Quart. J. Jpn. Weld. Soc. (993)