Warm Lateral Extrusion of Magnesium Wrought Alloy by using Multi-Axes Material Testing Machine

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1 Materials Science Forum Online: ISSN: , Vols , pp doi:1.428/ 25 Trans Tech Publications, Switzerland Warm Lateral Extrusion of Magnesium Wrought Alloy by using Multi-Axes Material Testing Machine Kanichi Hatsukano 1, a, Kunio Matsuzaki 2, b, Toru Shimizu 3, c and Kichitaro Shinozaki 4, c 1,2 3 and 4 National Institute of Advanced Industrial Science and Technology, Namikii, Tsukuba, Ibaraki, , Japan. a k.hatsukano@aist.go.jp, b k.matsuzki@aist.go.jp, c toru-shimizu@aist.go.jp, d k.shinozaki@aist.go.jp Keywords: Lateral extrusion, Warm extrusion, Counteracting pressure. Abstract. The Formability of magnesium wrought alloys, AZ61 and were investigated. First, the cylinder compression tests were carried out at room temperature and elevated temperatures. Then, the possibility of applying the warm lateral extrusion of the AZ61 and alloys were examined under several conditions by using the multi-axes material testing machine. A cylindrical billet coated with molybdenum disulfide lubricant was set in the horizontal die cavity and the billet was heated up to the extrusion temperature, and then extruded laterally under the two horizontally advancing punches. Furthermore, lateral extrusion with counteracting pressure on the end of branches by using two punches methods was tried to reduce the extrusion temperature and sound products was obtained around 19. Introduction Growing concern about global environmental problems, Mg alloys have attracted increasing interest as ecological materials. Mg alloys are the lightest materials among the structural metal and have excellent properties such as high specific strength, dimensional stability, electromagnetic interference shielding capability and recycleability. Most of the Mg alloy products are fabricated by casting process. The Mg wrought alloys, compared to cast Mg alloys, have advantages like superior mechanical properties, weldability and are useful for larger scale structural application. The development of net shape forming process for Mg alloys by using plastic deformation such as forging is expected to reduce environmental loads in manufacturing. However the formability of Mg wrought alloy is not known. We investigate the formability of the magnesium wrought alloy which is an extrusion and a forging alloy with high strength. Cylinder compression tests were carried out at room temperature and elevated temperatures to know flow stress and limitation of upsetting. On the other hand, the possibility of applying the warm lateral extrusion of the AZ61 and alloys were examined by using the multi-axes material testing machine [1]. Experiment Cylinder compression test at room and elevated temperature. The materials used in this study are commercial AZ61 and wrought alloys and the rods are obtained with 26mm in diametrer which is manufactured by extrusion at the temperature of 355. The rod in 26mm is turned into 16mm cylindrical billet by a lathe. The dimension of the cylindrical billet for compression test is 16 mm in diameter and 24 mm in height. The cylindrical billet was compressed with using parallel flat dies and non-lubrication at room temperature by the universal testing machine to obtain the mechanical properties. The autograph with All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-1/5/16,1::25)

2 488 Magnesium - Science, Technology and Applications having the furnace was used for the elevated compression test and the billet was also compressed at elevated temperatures to examine deformability. The multi-axes material testing machine and die set for net-shape forming. Fig. 1 shows the multi-axes material testing machine used in this study. The multi-axes material testing machine has four actuators in horizontal direction, and one in vertical direction. Fig.1 Multi- axes material testing machine. Fig.2 Die set for two branched parts Fig. 2 shows the experimental die sets for a warm near net-shape forming of automobile component such as spiders. The total cross section of this die branch is the same of the trunk. These dies and the punches are made of high speed steel (SKH 51). The band heaters are attached on both four outer square surfaces of upper and lower dies and also used four pipe-type heaters. The extrusion temperature is measured with an almel-chromel thermocouple thermometer. Measuring point is located on the surface of the lower die, 1 mm away from both edges of the trunk and the branch. The die set is cramped by using the vertical actuator in the center on the working area of the multi-axes material testing machine. Lateral extrusion by multi-axes material machine. The cylindrical billet with 16 mm in diameter and 5 mm in length is set in the horizontal die cavity and the billet is heated up to the extrusion temperature, and then extruded laterally under the two horizontally advancing punches. The lateral extrusion was done at the speed of 75mm /min. The billets were coated with molybdenum disulfide lubricant. To reduce the extrusion temperature is very important for Mg wrought alloy products owing to life span of die set, easier selection of the lubrication and treatment of working and etc. We tried the extrusion with counteracting pressure on the end of branches by using four punches. In applying the counteracting pressure process, after setting the die set which has the same diameter of trunk and branch, both center sides of the billet, branch portions are applied the counteracting stress of 75MPa to 2MPa and kept until the end of extrusion by the two punches at right angle to the two horizontally advancing punches, then extruded laterally under that two advancing punches. Results and Discussions The effect of temperature in cylinder compression test. Fig. 3 and fig.4 show the results of the cylinder compression test of both and AZ61 billets at room temperature and elevated temperatures. In the billet, the billets were broken with shear from room temperature to 18 with a small strain but over 19, the billet was easily deformed over.5 in deformation ratio. In the AZ61 billets, the billets were broken from room temperature to 16 in a small strain and the billet was easily deformed at 17 over.5 in deformation ratio[2]. The shape of the cylindrical billets compressed over 19 in the and 17 in the AZ61 look Billet, R.temp., 18, 19, 2, 25 Billet, R.temp.,16, 17, F ig.3 Result of compression test of Fig.4 Result of compression test of AZ61

3 Materials Science Forum Vols Nominal compression stress, ( Mpa ) 6 R.Temp Deformation degree. (%) Fig.5 Stress-strain diagram of like a mushroom with the top portion expanded larger than the lower portion. Fig.5 shows the nominal stress-strain diagrams of at various temperatures. At the room temperature, the speed of compression is.4 mm/min and at elevated temperatures, the speed of compression is.5mm/min. The stress of at room temperature rises steeply, yields around 171MPa and rises up again steeply to the maximum stress of 382MPa, then drops suddenly due to the cracks. The compressed billets until 18 show the crack with shear and break at the deformation ratio of below.21 but the compressed billets over 19 show no cracks and do not break until.5 strain. In the AZ61, the nominal stress-strain diagram shows the same temdancy of. But the billets beake from room temperature to 16 and do not break over 17. The effect of temperature in warm lateral extrusion. Fig. 6 and 7 show the products of and AZ61 at various temperatures. In the, the billet of Fig. 6 at 215 shows cracks with shear on each branch. The product at 23 and 26 do not show any cracks and are almost perfect but show a small dent at the top portion of the each branch. In the AZ61, the product at 22 and 23 show mainly one large crack on each branch and the product at 26 does not show any crack on each branch. In the lateral extrusion, after the occurrence of lateral metal flow, there is no large plastic metal flow. Hence, the billet is extruded laterally with relatively low forging pressure Fig.6 The products of at various tempratures Fig 7 The products of AZ61 at various tempratures Fig.8 shows the stress ram-displacement diagram of and AZ61 at various temperatures. The stress of the product with having the cracks decreases steeply after reaching the peak value compearing with that of the sound product. The effect of counteracting pressure. Fig 9 shows the products of with the various counteracting pressure. The product with 75MPa at 18 shows many cracks. The products with 75MPa at 19 and 2 show one crack on both branch and the deep of crack becomes shallower according to elevated temperature. The product with 75MPa at 22 is sound product. At 19, the product with 15MPa shows very shallow crack AZ Fig.8 The stress ram-displacement diagram at various temperatures

4 49 Magnesium - Science, Technology and Applications 8 18 /75MPa 19 /75MPa 2 /75MPa 22 /75MPa 19 /15MPa 19 /2MPa Fig.9 The products of with counteracting pressure mm/mim and 7.5mm/min from left to right. The product with 75mm/min at 215 has one crack on each branch and that of 35mm/min does have a crack but has a hollow on each end of the branch. The product with 7.5mm/min has no crack and is almost the perfect one. Conclusions but that with 2MPa are sound one. Fig.1 shows the stress ram-displacement diagram with counteracting pressure. The stress of the product with 15MPa at 19 drops steeply after peak value and a shallow crack occurred at end of the branch. The stress of the product with 2MPa shows almost the same tendency but no crack was observed. It was reported that the deformation of Mg material should be realized at the temperature above 225 [3]but in this study, sound products of Mg alloy were obtained around 19 by using the counteracting pressure. The effect of strain rate. Fig.11 shows the extruded products o f at various ram speed, 75mm/min, Cylinder compression test was carried out to obtain the mechanical properties of the Mg alloy. Then, the possibility of applying the warm lateral extrusion of the Mg alloy was examined by using the multi-axes material testing machine. The results obtained are as follows (1) In the billetof, the deformation ratio to failure reaches.11 at room temperature, but at above 19, it s flow stress decreases and the sample is easily deformed above.5 in deformation ratio without failure. (2) In the billet of AZ61, the sample is easily deformed above 17 with over.5 in strain. (3)The sound product of was obtained at the temperature of 23 and that of AZ61 obtained over 26 by the lateral extrusion. (4)The counteracting pressure methods have been done to reduce the extrusion temperature and the sound products was obtained below 19 with 2MPa. (5)The ram-desplacement speed is also effective to reduse the extrusion temperature. References 18 2MPa MPa 75MPa Fig 1 The stress -displacement diagram with counteracting pressure 75mm/min 36mm/min 7.5mm/min Fig 11 The product with various ram speed [1] K.Shinozki, (1987) Study on composite process cold extrusion on a multi-ram press. Report of Mechanical Engineering Laboratory, No.148. [2] K.Hatsukano et al.(24) Branched part forming of magnesium wrought alloy by warm lateral extrusion using multi-axes material testing machine the proceeding of 7th international coference deburring and surface finishing,pp [3] E. Doege and St. Janssen, (1999) Magnesium precision forming - experimental and numerical approach for magnesium near net-shape processing, Proceedings of 32nd ISATA, pp

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