Abstract
The effect of Cu coating metallic interlayer on the weldability, joint strength, and interfacial microstructure during high-power ultrasonic spot welding (HP-USW) of AZ31B Mg alloy has been studied. Interlayered samples exhibited good weldability and they resulted in strong sound joints with nearly the same strength as joints without interlayer, with the distinction of lower energy being required. The Cu interlayer affected the thermal and vibrational properties of the interface, as the maximum interface temperature decreased and approached better uniformity across the weld nugget. The base metal grain structure changed to equiaxed larger grains after ultrasonic welding and a chain of parent metal small grains were observed around the interface. A binary intermetallic compound product of Mg-Cu, which was rich in Mg, has been found around the interface that was diffused toward base metal. According to the electron probe micro-analyzer (EPMA) results, alongside temperature measurements and hardness data, the formation of Mg2Cu is suggested in this region. At the interface centerline, a narrow region was identified that was composed of Mg, Cu, and Al. Complementary transmission electron microscopy analysis estimated that Al-containing reaction product is a ternary alloy of the MgCuxAly type. The dispersion of fine grain intermetallic compounds as discrete particles inside Mg substrate in both interfacial regions formed a composite like structure that could participate in joint strengthening.
Highlights
Mg alloys are increasing in demand due to their high specific strength and they have attractive applications in automotive industries, aerospace, medical implants, electronic appliances, and sport equipment [1,2]
Commercial AZ31B rolled plates of magnesium alloy (3%Al, 1%Zn in wt%) with dimensions of mm in length, 20 mm in width, and thickness of 0.8 mm were used as the initial material
Final polishing resulted in a decrease of plate thickness, the applicable plate acetone prior to ultrasonic spot welding (USW)
Summary
Mg alloys are increasing in demand due to their high specific strength (strength to density ratio) and they have attractive applications in automotive industries, aerospace, medical implants, electronic appliances, and sport equipment [1,2]. The primary methods include tungsten arc welding (TIG), laser beam welding (LBW), resistance spot welding (RSW), electromagnetic welding (EMW), electron beam welding (EBW), diffusion bonding, soldering, brazing, adhesive bonding, and mechanical fastening. Like TIG, LBW, RSW, etc., have major problems that are mostly related to low boiling temperature of magnesium alloys that leads to porosities and hot cracking in the weld line and heat affected zone (HAZ). The development of solid-state processes, like friction stir welding (FSW), friction stir spot welding (FSSW), and ultrasonic spot welding (USW) helped to avoid problems that are related to melting and provide opportunities for dissimilar material welding [5,6,7]. FSW and FSSW have the limitations of making “keyhole” and the need to fixture and a long process time [5]
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