The microstructure characteristics and fracture behavior of the polyhedral primary iron-rich phase and plate-shaped eutectic iron-rich phase in a high-pressure die-cast AlSi10MnMg alloy

The characterization of multiple iron-rich phases in high-pressure die-cast AlSi10MnMg alloy was studied. Attention was focused on the formation and fracture behavior of the primary iron-rich phase ((P-IMC)I) formed in the shot sleeve and plate-shaped eutectic iron-rich phase in high-pressure die cast (HPDC) AlSi10MnMg alloy. Results show that multiple types of iron-rich phases with various morphologies, including primary iron-rich phases (polyhedral (P-IMC)I and (P-IMC)II) and eutectic iron-rich phases (plate-shaped, net shape, and fish-bone shape), were found in HPDC AlSi10MnMg. Coarse (P-IMC)I formed in the shot sleeve were distributed in the interface between primary α-Al and binary Al-Si eutectic. Small size (P-IMC)II and various eutectic iron-rich phases formed in the die cavity and they were distributed in Al-Si binary eutectic. The primary iron-rich phases belonged to a simple cubic crystal structure with a lattice constant a = 1.265 nm and they exhibited a lateral growth characteristic with a termination of {110} surface. β phase was surrounded by δ phase and they coexisted in a plate-shaped iron-rich phase. High-density stacking fault in β phase and δ/β interface provided an excellent nucleation site for δ phase. From mechanical behavior, the stress concentration caused by eutectic iron-rich phases was far less than (P-IMC)I and it would not cause crack initiation along the eutectic cluster boundary. In addition, (P-IMC)I showed the worst deformation coordination with primary α-Al while the plate-shaped eutectic iron-rich phase exhibited similar deformation characteristics with silicon particles.