Insight into the partial solutionisation of a high pressure die-cast Al-Mg-Zn-Si alloy for mechanical property enhancement

A partial solution treatment was investigated to enhance the mechanical properties for a die-cast Al-Mg-Zn-Si alloy. The strengthening mechanism was identified that the Mg₃₂(Al, Zn)₄₉ intermetallics and equilibrium η-MgZn₂ phase formed in the as-cast microstructure were partially dissolved into the α-Al matrix during solutionising and the fine semi-coherent η'-MgZn₂ phase was precipitated during subsequent aging. Consequently, the unique microstructure was characterised by the co-existence of equilibrium η-MgZn₂ phase and metastable η'-MgZn₂ phase in the α-Al matrix, together with the un-changed Mg₂Si eutectic and remnant Mg₃₂(Al, Zn)₄₉ intermetallics in the Al-Mg-Zn-Si alloy.