Application of shortened heat treatment cycles on A356 automotive brake calipers with respective globular and dendritic microstructures

Abstract

The conventional casting alloy A356 is probably one of the most popular alloys used for semi-solid metal (SSM) forming. This is due to its high fluidity and good castability. This alloy can be heat treated alternatively to the T4, T5 or T6 temper conditions. Previous work by the authors has shown that shorter heat treatment cycles can be applied for SSM processed A356 rather than the more costly traditional cycles (that were originally developed for liquid cast dendritic A356). The previous work was performed on relatively small rectangular plates (4×80×100mm3) that were cast in steel moulds with a 50 ton high pressure die casting (HPDC) machine. This work determined whether these short heat treatment cycles (T4, T5 and T6) can be applied successfully to a larger (and more complex) casting too. Since the automotive industry has many possible applications for SSM-HPDC parts, the newly developed heat treatment cycles, as well as the traditional heat treatment cycles, were applied to A356 brake calipers cast using a 630 ton HPDC machine. Vickers hardness measurements at a cross section of the brake calipers were performed, indicating that similar values can be obtained when using the significantly shorter heat treatment cycles. Finally, the typical tensile properties that can be obtained for SSM-HPDC A356 brake calipers are compared with those manufactured by gravity die casting. These results indicate that the differences in microstructures (globular or dendritic) do not have a noteworthy effect on the heat treatment response. This implies that the short heat treatment cycles originally developed for globular SSM-HPDC A356 castings can be successfully applied to dendritic liquid A356 castings too.