Strength of Thixoformed A319 Alloy at Elevated Temperature

When alloys are exposed to elevated temperatures they experience a decrement in their mechanical properties that leads to material failure. However, the use of thixoforming, an alternative metal processing method, could enhance mechanical properties by minimising the defects that exist in as-received alloys. Therefore, this study aimed to determine the tensile strength of thixoformed A319 under elevated temperatures by taking into account its intended use in vehicle cylinder head components. Thixoformed A319 was compared with as-received alloy manufactured by permanent mould casting. The cooling slope method was used to prepare the feedstock for thixoforming. The feedstock was reheated by induction heating until it reached 574 degrees C and was then formed in a mould. Afterwards, the as-received and thixoformed samples underwent T6 heat treatment. The resulting samples were characterised by using optical microscopy, scanning electron microscopy equipped with energy dispersive X-ray, X-ray diffraction analysis and a tensile test. Elevated temperature tensile tests were performed at 250 degrees C, in line with the temperature condition experienced by cylinder head components during operation. The ultimate tensile strength of the thixoformed samples was 30% higher than that of the as-received samples under elevated temperatures. Also, the analyses of the fracture surfaces showed that porosity, intermetallic compounds and impurities were amongst the failure factors for both alloys. Graphic

Automated summary

Alloys exposed to elevated temperatures often experience a decrease in mechanical properties, leading to material failure. Thixoforming, as an alternative metal processing method, can enhance mechanical properties by reducing defects. This study compared the tensile strength of thixoformed A319 with that of conventionally cast alloy, finding a 30% increase in ultimate tensile strength for thixoformed samples under elevated temperatures.