Joining of light hybrid constructions made of magnesium and aluminum alloys

Gas Tungsten Arc (GTA) and Electron Beam (EB) welding techniques have been used to study the weldability of Al-6063 to different cast Mg alloys (AM50 and AZ31). Four different electrodes (Al-1050, Al-4043, Al-10 wt.% Sr, and AZ92) were used as a filler metal. The welded samples were examined by metallographic techniques using both optical and scanning microscopy in combination with energy dispersive spectroscopy microanalysis (EDS). It was found that for the GTAW an eutectic microstructure was observed near the fusion line while as one approach the fusion zone center the β- Mg₁₇(Al, Zn)₁₂ became dominant. However for the Al-10 wt.% Sr, additional phases containing Sr were revealed. Heat Affected Zones - HAZ were developed, especially near the Mg side. In the Al side an enhanced grain boundary-GB, of Mg and Sr was observed. In contrast, a well-developed HAZ was observed on the Mg side. A formation of continuous brittle phase was observed in GB. The HAZ in Mg-AZ31 was of the order of several mm, while the HAZ adjacent to Mg AM50 was about a couple of hundreds μm. For EBW the β- Mg₁₇(Al, Zn)₁₂ phase was observed in the fusion zone while almost no HAZ was found. The presence of this inter-metallic phase in the fused zone is the main reason causing brittleness and low strength of the joints. There are indications that if a proper welding electrode composition will be used it may reduce this problem, and eventually enable the welding of dissimilar joints of aluminum and magnesium alloys. Using techniques which does not involved with melting and re-solidification in the fusion zone, such as Magnetic Pulse Welding, produce good joints.