Uneven distribution of cooling rate, microstructure and mechanical properties for A356-T6 wheels fabricated by low pressure die casting

Complex aluminum alloy part prepared by low pressure die casting (LPDC) usually has unevenly distributed microstructure and mechanical properties, which is related to the cooling conditions. To investigate the uneven characteristics of cooling rate, microstructure and mechanical properties of LPDC-fabricated A356-T6 wheels, the typical positions (including hub, spoke, outer flange, rim and inner flange) were selected to calculate the cooling rate by casting simulation. Then, the microstructure, mechanical properties, X-ray result and element content of these positions were analyzed in detail. The result shows that, the secondary dendrite arms spacing (SDAS), eutectic silicon and beta-Fe phase have the largest size at hub, and the eutectic silicon is plate-shaped when the cooling rate is 10 K/min, which results in poor ultimate tensile strength (UTS, 192 MPa) and elongation (2.1 %). While at the cooling rate of 100 K/min, refined microstructure, the disappearance of beta-Fe phases and the elimination of defects result in good mechanical properties of the outer flange. The UTS and elongation exceed 250 MPa and 13 %, respectively. The rim is more prone to occur shrinkage defects at high cooling rate, which results in mechanical properties that do not meet expectations. Furthermore, the Si, Mg, and Fe elements also exhibit uneven distribution in different positions of LPDC-fabricated A356-T6 wheels. The maximum deviation of Si element between the actual content and the standard content is as high as 21 %.