Influence of solidification rate on the microstructure, mechanical properties, and thermal conductivity of cast A319 Al alloy

Enhancing the strength and thermal conductivity of A319 aluminium alloy powertrain components can reduce instances of premature failure, by resisting or alleviating thermal stresses that develop during engine operation. These properties can be manipulated theoretically through microstructural control, for example via variation of the alloy solidification rate. Although increasing solidification rate has been observed to achieve improved mechanical properties, its influence on thermal conductivity is yet unclear. In this study, A319 alloy was cast with a succession of solidification rates by using a permanent mould preheated to a range of temperatures. The as-cast samples were comprehensively characterized in terms of their dendritic structures, secondary phase morphologies and area fractions, porosity, ultimate tensile strengths and Rockwell hardness values, and thermal conductivities, the latter of which was measured via the transient plane source method. The results demonstrated that refinement and other changes in microstructure with increasing solidification rate promoted no noticeable variation in thermal conductivity, despite improvements to strength and hardness. Thus, solidification rate can be controlled effectively to design the mechanical properties of A319 components without detriment to its thermal properties.