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

Abstract

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 θ (Al2Cu) were distributed in the α–Al grains, and the cross phases β (Mg2Si) grew near the grain boundary in the α–Al grains. Polygonal compounds φ (AlxTi9La2Ce6Cu) and irregular eutectic structures mainly formed by (α + 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 (α + 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 + φ → L + α + φ → L + (α + e) + α + φ → (α + e) + Q + α + φ → (α + e) + Q + [α + θ] + φ → (α + e) + Q + [α + θ + β] + φ