Abstract:Die-casting is a new magnesium/aluminum dissimilar welding process via casting liquid Mg alloy onto the solid Al alloy substrate. The difficulty of liquid-solid connection of magnesium/aluminum is the nature oxide layer on the solid Al alloy substrate surface that usually prevents metallurgical bonding between the magnesium and aluminum. During this process, the formation of some intermetallic compounds with a high hardness and brittleness over the interface would deteriorate the mechanical property of materials. The process of removing the oxide layer on solid Al substrate surface was investigated, and on this basis, the melt magnesium alloy was cast onto the solid aluminum alloy A390 by using home-made liquid-solid bimetal composite device. The effect of La on the structures and properties of the liquid-solid diffusion bonding interface of Mg/Al was researched. The results indicate that after adding the rare earth La into the magnesium alloys, β-Mg₁₇Al₁₂ at the interface of magnesium aluminum diffusion bonding gradually becomes less and thinner, and the cast grain is gradually refined. Most of La and Al combine to generate high melting point and high heat stability of rare earth phase-Al₁₁La₃ phase. When the magnesium alloys contain 1% rare earth La, the maximal shearing strength of the interface can achieve 88.5 MPa.

Key words: aluminum alloy; oxide layer; Mg/Al compound; La; interface structure