Effects of Main Alloying Elements on Interface Reaction between Tool Steel and Molten Aluminum

Effects of Si and Mg as main elements on interface reaction between tool steel and molten Al alloy at 700°C were investigated. Pure aluminum and Al-10mass%Mg alloy showed relatively simple interfacial layers, whereas thicker, multi-layered reaction bonds were found in the diffusion couple of A380 alloy. The diffusion of a large amount of Fe into Al matrix throughout the interfacial layer led to the formation of Al-Fe based intermetallic particles in the Al base metals. The diffusion couple of Al-10mass%Mg alloy showed a similar intermetallic layer as that of pure Al, indicating that 10mass%Mg in the Al melt rarely affected the formation of Al-Fe intermetallic layers. However, A380 alloy showed much expanded soldering area and increased thickness of intermetallic layers. Based on the phase diagram calculated, the solubility of Fe in liquid Al increased significantly with increasing Si content up to apploximately 5mass%, while, in the case of 10mass%Mg addition, the Fe solubility gradually decreased with increasing Mg content. Al-10mass%Mg alloy also showed the same tendency as that of pure Al in the formation and distribution of intermetallic compounds. However, in the Al-12mass%Si alloy, two types of Al-Fe-Si ternary compounds are present on the Al-rich side.