Study on non-equilibrium solidification microstructure of Al-Cu3-Si-Mg alloy by MMDF

Al-Cu3-Si-Mg wheel hubs were prepared by molten metals die forging (MMDF). The as-cast microstructure morphology of the alloy formed under pressure was observed by optical microscope and scanning electron microscope. The granular phases theta (Al2Cu) were distributed in the alpha-Al grains, and the cross phases beta (Mg2Si) grew near the grain boundary in the alpha-Al grains. Polygonal compounds phi (AlxTi9La2Ce6Cu) and irregular eutectic structures mainly formed by (alpha + Al2Cu) eutectic formed under non-equilibrium solidification were found at the grain boundaries. Q (Al5Cu2Mg8Si6) phases were found at the intersection of grain boundaries. With the increase of pressure, the proportion of irregular eutectic structures (alpha + Al2Cu) decreased from 7.3% to 5.2%. Combined with microstructure analysis and thermodynamic software analysis, the non-equilibrium solidification path was determined as follows: L -> L + phi -> L + alpha + phi -> L + (alpha + e) + alpha + phi -> (alpha + e) + Q + alpha + phi -> (alpha + e) + Q + [alpha + theta] + phi -> (alpha + e) + Q + [alpha + theta + beta] + phi