Influence of Silicon on Intergranular Corrosion for Aluminum Alloy*

Transcription

1 UACJ Technical Reports, Vol.1 21 pp 論 文 Influence of Silicon on Intergranular Corrosion for Aluminum Alloy* Yoshiyuki Oya** and Yoichi Kojima** An alternative fluorocarbon refrigerant of a heat exchanger of a car air conditioner may change to carbon dioxide refrigerant which has lower global warming potential than the alternative fluorocarbon refrigerant. If carbon dioxide is used as a refrigerant, both pressure and temperature of a heat exchanger will become higher. Silicon is a potential element added to aluminum to use for the heat exchangers with carbon dioxide refrigerant because of increase in tensile strength. The operation temperature affects metallographic structure of aluminum-silicon alloy, might leading to intergranular corrosion. To investigate influence of Si concentration and heat treatment at 3 K on susceptibility to intergranular corrosion, in various alloys, electrochemical measurements and observation of the metal textures were performed. The susceptibility to intergranular corrosion increased with increase in Si concentration and increased with heat treatment time at 3 K once, but turned to decrease by long term heat treatment at 3 K. Addition of Mg and Mn promoted generation and disappearance of susceptibility to intergranular corrosion in Al-Si alloy. Si precipitates were observed by TEM. Without and with short heat treatment at 3 K, small Si precipitates were observed on grain boundary and could not observe precipitate in grain. With long heat treatment at 3 K, large Si precipitates were observed in grains and on grain boundaries. Short heat treatment at 3 K formed continuous Si depleted layer along grain boundaries. The Si depleted layer increased susceptibility to intergranular corrosion. However, long heat treatment at 3 K decreased the susceptibility to intergranular corrosion. Addition of Mg and Mn affects precipitation of Si precipitates. It is suggested that the susceptibility to intergranular corrosion had dependence of addition of Mg and Mn. Keywords: aluminum alloy, intergranular corrosion, brazing process, heat treatment １ Introduction aluminum alloys for increasing in tensile strength. Aluminum-manganese (Al-Mn) series aluminum However, when the high strength Al-Mn series alloys which are representative as 33 and 323 alloy aluminum alloys with Cu and Si are applied to the are widely used for materials of heat exchangers heat exchanger with the CO2 refrigerant, solute because of high tensile strength and corrosion elements are precipitated preferentially on a grain resistance. Heat exchangers in car air conditioners boundary because the operation temperature reaches are produced by a brazing process and CFC-13a to 3 K 1). The precipitation induces the concentration (CH2FCF3) is used as refrigerant. The refrigerant may difference between the grain and grain boundaries, change to carbon dioxide (CO2) which has lower might leading to intergranular corrosion. global warming potential than the alternative Al-Mn series aluminum alloys have comparatively fluorocarbon refrigerant1). If CO2 is used as the low susceptibility to intergranular corrosion although refrigerant, both pressure and temperature in the the susceptibility increases due to heat treatment and heat exchanger would become higher. Copper (Cu) addition of alloy elements 2)-). The heat treatment such * ** 8 and silicon (Si) are often added to Al-Mn series This paper is reprinted from Mater. Trans. (213), No. 2 Department, Fukaya Center, Research & Development Division, UACJ Corporation UACJ Technical Reports Vol.1 21

2 Influence of Silicon on Intergranular Corrosion for Aluminum Alloy as at more than 673 K at which Al6Mn and/or susceptibility to intergranular corrosion. In this study, Al 6 (MnFe) precipitate preferentially on grain it is investigated that Si concentration and heat boundaries forms Mn depleted layer along grain treatment time at 3 K after brazing process affect boundaries. Preferential corrosion of the Mn depleted the susceptibility to intergranular corrosion using layer causes the intergranular corrosion. In an Al-Mn various alloys. alloy Cu as an alloy element and iron (Fe) as an impurity enhanced susceptibility to intergranular corrosion 2), 3) ２ Experimental Procedure but Si inhibited susceptibility to 2.1 intergranular corrosion). Process and materials A mechanism about generation of intergranular Chemical compositions of specimens are shown in corrosion has been investigated carefully for Al-Cu Table 1. All specimens were cast in book mold, alloys ). Heat treatment at which Al2Cu intermetallic homogenized at 873 K for s, hot rolled at compound precipitates on grain boundaries 793 K to 3. mm thickness, and then cold rolled to preferentially forms Cu depleted layer along grain 1 mm thickness. The sheets were annealed at 673 K boundaries. This is reason why the diffusion rate of for s. The annealed sheets were heat- Cu on grain boundaries is higher than that in grains. treated at 873 K for 18 s which corresponded to a Since solute Cu makes pitting potential (E PIT ) of brazing process. Finally, the brazed sheets were aluminum alloy noble, E PIT of the grain boundary is reheated at 3 K which is the maximum working lower than that of the grains. Difference in E PIT temperature for CO2 air conditioners for s. between the grain and grain boundary causes The heat-treated time at 3 K after brazing process intergranular corrosion. Thus, it means that addition is regarded as HTT t HT in this paper. of Cu in aluminum alloy is harmful for the intergranular corrosion. However, tensile strength of Al-Mn alloys 2.2 without Cu is intolerably low for usage of the heat Distribution of precipitated intermetallic compounds exchanger with CO2 refrigerant. Addition of other near grain boundaries of the specimens heat-treated elements to increase tensile strength is imperative. at 3 K was observed by TEM (JEOL Ltd., JEM- Si is a major element added to aluminum alloy. Si in TEM observation 31FEF, accelerating voltage: 3 kv). aluminum alloy contributes to increase tensile strength due to solid solution and precipitation strengthening. The precipitation of the various intermetallic 2.3 E valuations of susceptibility to intergranular corrosion compounds containing Si was affected by heat Susceptibility to intergranular corrosion was treatment meaning that susceptibility to intergranular evaluated by anodic dissolution. A Pt plate was used corrosion also changed as a counter electrode. Test solution was mass% 6)-11). The intergranular corrosion was not observed for water quenched Al-Si 8) and Al-Si-Mg 6), 7), 9) alloys but was observed for air cooled Al-Si 8), Al-Si-Mg 6), 1) and Al-Si-Mn 11). Heat treatment increased in susceptibility to intergranular corrosion for Al-Si-Mg 6), 7), 9) and Al-Si-Mn 1), 11). These intergranular corrosion were caused by dissolution of Mg2Si intermetallic compound on grain boundary in Al-Si-Mg 7), 9) or Si depleted layer along grain boundary in Al-Si and Al-Mn-Si alloys 6), 8), 1), 11). It means that the cause of the intergranular corrosion depended on the type of alloys. However, there are few reports about systematic study about influence of Si concentration in various alloys and heat treatment conditions on Table 1 Chemical compositions of specimens. mass%.si.8si 1.2Si 1.Si.2Mg-.9Si.2Mg-1.3Si Mn-.Si Mn-.8Si Mn-1.2Si Mn-1.Si Mn-.2Mg-.6Si Mn-.2Mg-.8Si Mn-.2Mg-1.2Si Mn-.2Mg-1.Si Si Fe Cu Mn Mg Al UACJ Technical Reports Vol

3 (after this, mass% is shortened to %) NaCl adjusted morphology depended on Si concentration. Pitting ph to 3 by acetic acid. The specimens were corrosion was observed for.si and.8si and immersed in % NaOH at 333 K for 3 s, rinsed with intergranular corrosion was observed for 1.2Si. At t HT distilled water, immersed in a 3% HNO3 at 298 K for = s, pitting corrosion was observed for 6 s and then rinsed with distilled water as a.si, while intergranular corrosion was observed for pretreatment. Applied anodic current density was 1.8Si and 1.2Si. The corrosion depth at t HT = Am-2 at which the specimens were polarized to the s was deeper than that at t HT = s. Corrosion potential which is higher than E PIT. The polarization morphology was independent of Si concentration, time is s. After the anodic dissolution, cross being pitting corrosion at t HT = s. section of the center of the specimen with optical Fig. 2 shows relationships between HTT and microscope was observed for identifying corrosion corrosion depth for.si,.8si, 1.2Si, and 1.Si. The morphology and measuring corrosion depth. In this open and solid symbols show pitting corrosion and paper, the corrosion depth means the maximum intergranular corrosion, respectively. If the current depth from surface to the bottom of corrosion in efficiency is constant in anodic dissolution regardless observed 3 views. of corrosion morphology, the volume of dissolved aluminum is constant in anodic dissolution applying constant current density, the corrosion depth would ３ Results 3.1 show a tendency of intergranular corrosion. The Al-Si alloys 3. corrosion depth of.si was independent of HTT, Susceptibility to intergranular corrosion being about. 1- m. The corrosion morphology of Fig. 1 shows optical micrographs of the cross section.si is pitting corrosion. The corrosion depth and after anodic dissolution for.si,.8si, and 1.2Si at t HT morphology of.8si, 1.2Si, and 1.Si depended on =, and s. At t HT = s, corrosion HTT. For.8Si, corrosion morphology was pitting 6 corrosion at t HT = s. Corrosion depth increased at.si.8si 1.2Si t HT s although the intergranular corrosion was observed at t HT 6. 1 s. Furthermore, the corrosion morphology was pitting tht= s corrosion again at t HT = s. For 1.2Si and 1.Si, intergranular corrosion was observed at t HT = 6. 1 s, corrosion morphology was pitting tht= s 7 Corrosion depth, D / µm tht= s Fig. 1 1 PC 6 IGC.Si.8Si 1.2Si 1.Si µm Optical micrographs of the cross section after anodic dissolution for.si,.8si, and 1.2Si at t HT =, and s. UACJ Technical Reports Vol HTT, t HT / s Fig. 2 Relationships between HTT and corrosion depth for.si,.8si, 1.2Si, and 1.Si. Pitting corrosion and intergranular corrosion are denoted as PC and IGC, respectively.

4 Influence of Silicon on Intergranular Corrosion for Aluminum Alloy.2Mg -.9Si corrosion at t HT = s. Corrosion depth was.2mg - 1.3Si the deepest at t HT = or s and then tht= s decreased rapidly with increase in HTT. That is, susceptibility to intergranular corrosion showed peak at t HT = s for.8si and 1.2Si and at t HT = s for 1.Si. TEM observation tht= s Fig. 3 shows bright field TEM images of precipitates on grain boundaries for 1.2Si at t HT = and s. At t HT = s, Si precipitates with diameter of about m were observed on grain boundaries and could not be observed in grain. On the other hand, tht= s Si precipitates with diameter of about 1 1- m were observed in grains and on grain boundaries at t HT = s. This indicates that precipitation and growth of Si precipitates occurred by the heat treatment at 3 K Fig. Al-.2%Mg-Si alloys Susceptibility to intergranular corrosion Fig. shows optical micrographs of the cross section 1 µm Optical micrographs of the cross section after anodic dissolution for.2mg-.9si and -1.3Si at t HT =, and s. after anodic dissolution for.2mg-.9si and -1.3Si at t HT =, 8.6 1, and s. Corrosion and solid symbols show pitting corrosion and morphology depended on Si concentration at t HT = s. intergranular corrosion, respectively. Both the corrosion Pitting corrosion was observed for.2mg-.9si and depth and corrosion morphology depended on HTT. intergranular corrosion was observed for.2mg-1.3si. For.2Mg-.9Si, the corrosion morphology was pitting At t HT = s, obvious intergranular corrosion corrosion at t HT = and s. The corrosion w a s o b s e r v e d f o r.2m g -.9S i a n d c o r r o s i o n morphology was intergranular corrosion at t HT = 1. morphology was pitting corrosion for.2mg-1.3si. At s. The corrosion depth increased t HT = s, corrosion morphology was pitting with increase in HTT and showed the maximum at t HT corrosion in each Si concentration. = s. However, the intergranular corrosion Fig. shows relationships between HTT and the w a s o bs e r ve d unt il t H T = s a nd the corrosion depth for.2mg-.9si and -1.3Si. The open corrosion depth decreased. The corrosion morphology was pitting corrosion again at t HT =.61 1 s. For tht= s tht= s.2mg-1.3si, the intergranular corrosion was observed at t HT = s. The corrosion depth increased with HTT. The corrosion morphology was pitting corrosion at t HT = s and corrosion depth decreased rapidly with HTT. That is, the susceptibility to intergranular corrosion of.2mg-.9si and -1.3Si showed peak at t HT = and s, respectively. 1 µm Fig. 3 1 µm Bright field TEM images of precipitates on grain boundaries for 1.2Si at t HT = and s TEM observation Fig. 6 shows bright field TEM images of precipitates UACJ Technical Reports Vol

5 on grain boundaries for.2mg-1.3si at t HT = Si and intergranular corrosion was observed for and s. At t HT = s, Si precipitates Mn-1.Si. At t HT = s, pitting corrosion with diameter of about 1 m were observed on was observed for Mn-.Si, intergranular corrosion the grain boundary and could not be observed in the was observed for Mn-.8Si and -1.Si. At t HT = 2.9 grain. A precipitate free zone (PFZ) along grain 1 6 s, the corrosion morphology was pitting boundary was observed. At t HT = s, Si corrosion in each Si concentration. -8 precipitates with diameter of about 1 1 m on the Fig. 8 shows relationship between HTT and grain boundary and about a few 1 m in the grain corrosion depth for Mn-.Si, -.8Si, -1.2Si, and -1.Si were observed. This indicates that Si precipitated and grew by the heat treatment at 3 K. PFZ was also Mn -.Si 3.3 Al-%Mn-Si alloys Susceptibility to intergranular corrosion Fig. 7 shows optical micrographs of the cross section Mn -.8Si Mn -1.Si tht= s observed at s. after anodic dissolution for Mn-.Si, -.8Si, and -1.Si morphology depended on Si concentration at t HT = s. Pitting corrosion was observed for Mn-.Si and PC IGC 3.2Mg-.9Si.2Mg-1.3Si tht= s Corrosion depth, D / µm tht= s at t HT =, 8.6 1, and s. The corrosion µm Optical micrographs of the cross section after anodic dissolution for Mn-.Si, -.8Si, and -1.Si at t HT =, 8.6 1, and s. Fig. 7 HTT, t HT / s Relationships between HTT and the corrosion depth for.2mg-.9si and -1.3Si. Pitting corrosion and intergranular corrosion are denoted as PC and IGC, respectively. tht= s tht = s Corrosion depth, D / µm Fig. PC IGC 3 3 Mn-.Si Mn-.8Si Mn-1.2Si Mn-1.Si µm Fig UACJ Technical Reports Vol HTT, t HT / s.2 µm Bright field TEM images of precipitates on grain boundaries for.2mg-1.3si at t HT = and s. 1 3 Fig. 8 Relationship between HTT and corrosion depth for Mn-.Si, -.8Si, -1.2Si, and -1.Si. Pitting corrosion and intergranular corrosion are denoted as PC and IGC, respectively.

6 Influence of Silicon on Intergranular Corrosion for Aluminum Alloy The open and solid symbols show pitting corrosion and observed on Al-Mn series intermetallic compounds, intergranular corrosion, respectively. The corrosion being Si precipitates identified by elemental analysis. depth and morphology of Mn-.Si were independent It is suggested that Si precipitated and grew by the of HTT while the corrosion depth and morphology of heat treatment at 3 K. Mn-.8Si, -1.2Si, and -1.Si depended on HTT. For Mn-.8Si, corrosion morphology was pitting 3. Al-%Mn-.2%Mg-Si alloys corrosion at t HT = and s. and intergranular 3..1 corrosion at t HT = 1. 1 s. Corrosion morphology Fig. 1 shows optical micrographs of the cross 3 was pitting corrosion again at t HT = 6. 1 s. Susceptibility to intergranular corrosion section after anodic dissolution for Mn-.2Mg- For Mn-1.2Si, the corrosion morphology was.6si, -.8Si, and -1.Si at t HT =, 8.6 1, and pitting corrosion at t HT = s and the intergranular s. Corrosion morphology depended on Si c o r r o s i o n a t t H T = s. T h e concentration at t HT = s. Pitting corrosion was Corrosion morphology was pitting corrosion again at o b s e r v e d f o r M n -.2M g -.6S i a n d -.8S i a n d t HT = 6. 1 s. The corrosion depth was the intergranular corrosion was observed for -1.Si. The deepest at t HT = s and decreased with pitting corrosion was observed for Mn-.2Mg-.6Si increase in HTT. For Mn-1.Si, intergranular and intergranular corrosion for -.8Si and -1.Si at t HT corrosion was observed at t HT = s, = s. At t HT = s, the corrosion corrosion morphology was pitting corrosion at t HT = morphology was pitting corrosion in each Si 6. 1 s. Corrosion depth was the deepest at t HT = concentration s and then decreased rapidly with increase Fig.11 shows relationships between HTT and in HTT. That is, susceptibility to intergranular corrosion depth for Mn-.2Mg-.6Si, -.8Si, -1.2Si, corrosion of Mn-1.2Si and -1.Si showed a peak at and -1.Si. The open and solid symbols show pitting t HT = and s, respectively Mn -.2Mg -.6Si TEM observation Fig. 9 shows bright field TEM images of Mn -.2Mg -.8Si Mn -.2Mg -1.Si = and s. Intermetallic compounds observed at t HT = s were Al-Mn series intermetallic compounds with gray spherical or elliptical shape. tht= s precipitates on grain boundaries for Mn-1.2Si at t HT The distribution of Al-Mn series intermetallic tht = s 1 µm Fig. 9 tht = s 1 µm Bright field TEM images of precipitates on grain boundaries for Mn-1.2Si at t HT = and s. tht= s to that at t HT = s. Dark black compounds were also tht= s compounds at t HT = s was the almost same 1 µm Fig. 1 Optical micrographs of the cross section after anodic dissolution for Mn-.2Mg-.6Si, -.8Si, and -1.Si at t HT =, 8.6 1, and s. UACJ Technical Reports Vol

7 PC Corrosion depth, D / µm IGC 3 3 corrosion increased with increase in Si concentration. Mn-.2Mg-.6Si Mn-.2Mg-.8Si Mn-.2Mg-1.2Si Mn-.2Mg-1.Si Therefore the intergranular corrosion which occurred at t HT = s was caused by Si. Because solute Si makes E PIT of aluminum noble as well as 2 2 solute Cu12), it is thought that a mechanism of 1 generation of susceptibility to the intergranular 1 corrosion caused by Si is the same as that caused by Cu. According to the mechanism about the generation of the intergranular corrosion in Al-Cu alloys, the HTT, t HT / s intergranular corrosion is preferential corrosion on Fig. 11 Relationships between HTT and corrosion depth for Mn-.2Mg-.6Si, -.8Si, -1.2Si, and -1.Si. Pitting corrosion and intergranular corrosion are denoted as PC and IGC, respectively. grain boundaries caused by difference of E PIT between a grain and Cu depleted layer along a grain boundary. Thus, it is suggested that the intergranular corrosion in Al-Si alloys is generated by the Si depleted layer along a grain boundary. It is expected corrosion and intergranular corrosion, respectively. that corrosion depth of intergranular corrosion will For Mn-.2Mg-.6Si, the corrosion depth was increased with Si concentration because of formation independent of HTT and the morphology was pitting of continuous Si depleted layer and increase in corrosion in spite of HTT. The corrosion depth and difference of E PIT between grain and Si depleted layer m o r p h o l o g y o f M n -.2M g -.8S i, -1.2S i, a n d along grain boundary leading to preferential -1.Si depended on HTT. For Mn-.2Mg-.8Si, dissolution of grain boundaries. This tendency was corrosion morphology was pitting corrosion at t HT = found in Fig. 2. As shown in Fig. 2, corrosion depth s and intergranular corrosion at t HT = s. increased once and turned to decrease with HTT. Corrosion morphology was pitting corrosion again at This mechanism, in which corrosion depth had such t HT = 6. 1 s. The corrosion depth at t HT = 2.88 HTT dependence, is thought as following. Si 1 s was the deepest within HTT. For Mn-.2Mg- precipitates on grain boundaries at cooling process 1.2Si, the intergranular corrosion was observed at t HT after brazing and heat treatment at 3 K, and Si = 3. 1 s. The corrosion morphology was depleted layer along grain boundaries is formed pitting corrosion at t HT = 6. 1 s. Corrosion depth continuously. The continuous Si depleted layer causes a t t HT = s was the deepest. For intergranular corrosion. However, the heat treatment Mn-.2Mg-1.Si, intergranular corrosion was for a long time not only precipitates on grain o b s e r v e d a t t H T = s, corrosion boundaries but also in grain caused to decrease in morphology was pitting corrosion at t HT = s. solute Si concentration. The Si concentration in the Corrosion depth at t HT = s was the deepest grain continues to decrease until attaining to the and then the corrosion depth decreased rapidly. That concentration on the grain boundary. It means that is, susceptibility to intergranular corrosion of the pitting potentials in the grain and the grain Mn-.2Mg-.8Si, -1.2Si, and -1.Si showed peak at t HT boundary become the same. Thus, corrosion = s. progresses in both the grain and the grain boundary, indicating that the corrosion depth decreases and the susceptibility to intergranular corrosion disappear. To ４ Discussions confirm mechanism, Fig. 12 shows STEM-EDS line As shown in Fig. 1 and Fig. 2,.Si did not have analysis for Si on grain boundary for 1.Si at t HT = intergranular corrosion susceptibility regardless of and s. At t HT = s, Si intensity decreased HTT. Al-Si alloy containing more than.%si showed around grain boundary. The decrease in Si intensity the intergranular corrosion at t HT or s. corresponded to Si depleted layer along a grain It is clear that the susceptibility to intergranular boundary. At t HT = s, deference in Si 1 UACJ Technical Reports Vol.1 21

8 Influence of Silicon on Intergranular Corrosion for Aluminum Alloy intensity between grain and grain boundary was not corrosion to pitting corrosion, little depended on Si observed. concentration. These were the longest for Al-Si alloys As shown in Fig. 6 and Fig. 9, regardless of alloy and were shortened by other alloy element. This is elements, precipitation and growth of Si precipitates reason why the addition of Mn and Mg induces occurred by the heat treatment at 3 K. It is promoted precipitation of some kinds of intermetallic thought that generation and disappearance of the compounds. These intermetallic compounds promoted intergranular corrosion were caused by Si depleted precipitation of Si precipitates because these layer along a grain boundary for Al-.2%Mg-Si alloys intermetallic compounds became a nucleation site. as mentioned in 3.2, Al-%Mn-Si alloys in 3.3, and Al-%Mn-.2%Mg-Si alloys in 3. in the same as Al-Si ５. Conclusions alloys. Fig. 13 shows relationships between HTT, when corrosion depth is the deepest, or corrosion We investigated that susceptibility to intergranular morphology changes from intergranular corrosion to corrosion of Al-Si alloys, Al-.2%Mg-Si alloys, pitting corrosion, and Si concentration for specimens. Al-%Mn-Si alloys and Al-%Mn-.2%Mg-Si alloys HTT, when corrosion depth is the deepest or heat-treated at 3 K after brazing process. For a corrosion morphology changes from intergranular mechanism of generation and disappearance of susceptibility to intergranular corrosion, following conclusions were drawn. (1) A d d i t i o n o f S i c a u s e d s u s c e p t i b i l i t y t o intergranular corrosion for each alloy series. Si intensity, ISi /a.u. Susceptibility to intergranular corrosion was observed for the as-brazed specimen containing higher than 1.2%Si. (2) Susceptibility to intergranular corrosion increased with increase in the heat treatment t HT= s t HT= s time at 3 K once, but turned to decrease. Grain boundary 6 7 (3) S h o r t h e a t t r e a t m e n t a t 3 K c a u s e d 8 precipitation and growth of Si precipitates on 9 1 grain boundaries and then continuous Si Distance, d /nm depleted layer along grain boundaries was 1 7 formed. Si precipitates were also precipitated 1 7 (a) Al-Si Al-.2Mg-Si Al-Mn-Si Al-Mn-.2Mg-Si 1 HTT(IGC/PIT), tht (IGC/PIT) / s HTT(max, depth), t HT (max, depth) / s Fig. 12 STEM-EDS line analysis for Si on a grain boundary for 1.Si at t HT = and s. (b) Al-Si Al-.2Mg-Si Al-Mn-Si 1 6 Al-Mn-.2Mg-Si Si content, C Si mass% Si content, C Si mass% Fig. 13 Relationships between HTT, when (a) corrosion depth is the deepest, or (b) corrosion morphology changes from intergranular corrosion to pitting corrosion, and Si concentration for specimens. UACJ Technical Reports Vol

9 in grain at long term heat treatment at 3 K, solute Si concentration in a grain decreased to that on a grain boundary. This is reason why the susceptibility to intergranular corrosion had time dependence. () Addition of Mg and Mn promoted generation of susceptibility to intergranular corrosion because Mg 2Si intermetallic compounds and Al-Mn series intermetallic compounds promoted precipitation of Si precipitates. () Addition of Mg and Mn promoted disappearance of susceptibility to intergranular corrosion the same as generation. Yoshiyuki Oya No. 2 Department, Fukaya Center, Research & Development Division, UACJ Corporation Yoichi Kojima No. 2 Department, Fukaya Center, Research & Development Division, UACJ Corporation References 1) J. K. Kunesch: Proceedings of the 2nd International Congress Aluminium Brazing, (Aluminium Verl., Hotel Nikko, Düsseldorf, 22), pp ) M. Kaifu, H. Fujimoto and M. Takemoto: J. Japan Inst. Met. 32 (1982), ) K. Tohma: J. Japan Inst. Met. 36 (1986), ) M. Zamin: Corrosion 37 (1981), ) J. R. Galvele and S. M. De De Michel: Corros. Sci. 1 (197), ) M. H. Larsen, J. C. Walmsley, O. Lunder and K. Nisancioglu: J. Electorchem. Soc. 17 (21), C61-C68. 7) K. Tohma, Y. Sugai and Y. Takeuchi: J. Japan Inst. Met. 31 (1981), ) K. Tohma: J. Japan Inst. Met. 3 (198), ) K. Yamaguchi and K. Tohma: J. Japan Inst. Met. 7 (1997), ) S. Iwao and M. Asano: J. Japan Inst. Met. 9 (29), ) S. Iwao, M. Edo and S. Kuroda: J. Japan Inst. Met. 6 (21), ) J. R. Davis: Corrosion of Aluminum and Aluminum Alloys, (ASM International, Ohio, 1999), pp UACJ Technical Reports,Vol.1 (21)