Solid-Solution Evolution Behavior of Al-Cu3-Si-Mg During the MMDF Process

Al-Cu3-Si-Mg alloy prepared by molten metal die forging (MMDF) under a pressure of 118 MPa was solution-treated at different temperatures and times, and the evolution behavior of the non-equilibrium eutectic in the microstructure was observed using an optical microscope and scanning electron microscope. The results show that the initial solidification structure of Al-Cu3-Si-Mg before solution treatment consists of irregular eutectic (α+Al2Cu), strip compound Q (Al5Cu2Mg8Si6), polygonal phase φ(AlxTi9La2Ce6Cu), spherical particle θ(Al2Cu) and cross-shaped β(Mg2Si) near the grain boundary. After solution treatments, the irregular eutectic at grain boundaries is dissolved. In the solution temperature range of 480 °C~510 °C, the irregular eutectic fraction decreased with the increase in solution temperature, and the grain size of other compounds such as Q (Al5Cu2Mg8Si6) and the spherical particle phase θ(Al2Cu) also showed a decreasing trend. However, all phases do not change significantly with the increase in solution temperature when the solution temperature is between 510 °C and 540 °C. It was determined experimentally that the holding time of 30 min at each temperature is the solution limit. Based on the experimental results, a dissolution model of intergranular irregular eutectic was established as dEdt=−4PπtD+2rkkPD.