Soldering of Mg Joints Using Zn-Al Solders
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TRODUCTION
CHANGES to the electrical engine, which can bring about a reduction in its mass, are of significant interest to the automotive industry.[1,2] Al and Mg alloys are increasingly used to reduce structural mass.[3] Taking into account the lightest applications, the density of structural materials (qAl = 2.7 g cm 3, qMg = 1.7 g cm 3)[4] is very important. The aerospace industry’s requirements for lightweight materials to operate under increasingly demanding conditions calls for reduced mass and improved mechanical properties. Compared to the Al alloys, the Mg alloys display better physical and mechanical properties, such as high strength-to-weight ratio, high damping capacity, and a high recycling potential. These facts could have a decisive effect on the application of Mg alloys in the automotive, electronics, and aerospace industries. However, similar atomic mass and melting temperature in the Al-Mg system formed brittle intermetallic compounds (IMCs) such as Al3Mg2 and Al12Mg17 in the solidified metal.[5] Furthermore, joining the Al with Mg alloys is difficult, but possible using several
TOMASZ GANCARZ, WOJCIECH SKUZA, and KATARZYNA JANIK are with the Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 30-059 Krakow, Poland. Contact e-mail: [email protected] KATARZYNA BERENT is with the AGH University of Science and Technology, Academic Centre for Materials and Nanotechnology, 30-059 Krakow, Poland. Manuscript submitted May 24, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
techniques such as resistant spot welding,[3,6] reactive brazing,[7] laser welding,[8] ultrasonic-assisted soldering,[9] and so on. In order to eliminate the negative effect of Mg–Al IMCs on the strength of the joints, an interlayer intended to block the formation of brittle IMC[3] was used. Zn,[3] Sn-Zn alloys,[10] Mg-Zn-Al, and Mg-In-Zn[11] were used to join Al with Mg alloys. In view of the high oxidation and corrosion of Mg alloys, an addition characterized by high electrode potential compared to Mg ( 2.37 V)[9] is made to the solder. In this case, the layers of chromium and Teflon protected the Mg against corrosion.[12] Mg alloys soldered at high temperature displayed worse mechanical properties, so the joining process temperature should be lower than 450 C. For lower temperature soldering, flux was used to increase wettability, which also protected the alloy surface from the formation the stable magnesium oxide.[11] The application of an Zn interlayer when joining Al/Mg alloys using resistant spot welding caused a reduction in welding current compared with traditional welding.[3] Al dissolving into the fusion zone caused the increased formation of solid particles, which improves the quality of the joints.[3] Sn-Zn used at low temperatures for soldering Al/Mg joints caused the amount of Zn to rise by up to 30 pct, increasing shear strength. In addition, the dispersive distribution of the Al-Sn-Zn solid solution within the solder reduced the brittleness of the joint, thus greatly improving the mechanical properti
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