MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A390 ALLOY HOLLOW BILLET FABRICATED BY DIRECT CHILL CASTING

A390 alloy hollow billet fabricated by DC casting process was studied by numerical simulation and experiment. The microstructure and mechanical property were investigated by means of optical microscopy, scanning electron microscopy (SEM), tensile and hardness tests. The simulated result showed that temperature of solidification shell at the inner wall would recover to mushy zone during solidification. This is consistent with experimental results that the inner wall is rough due to Al-Si-Cu and Al-Si eutectics penetrate out the inner wall of A390 hollow billet. In addition, this benefits to no hanging would happen due to relative low solidification shrinkage at the inner wall. Fine primary Si particles were uniformly distributed in the hollow billet as image analysis result showed that the primary Si panicles have an average size of 22.9-25.82 pm and area fraction of 10.35-11.24% in the hollow billet. The tensile strength of the hollow billet was more than 256.3 MPa in as-cast condition and increased to more than 410.9 MPa after T6 heat treatment. The strengths and hardness of the DC-casted A390 alloy are higher than the conventional processes such as sand casting and permanent mold casting. The current study may provides a potential application for cylinder liner in the automotive industry after an adequate extrusion process.