A study of precipitation behaviour of A356 alloy using ultrasonic velocity measurements

Abstract

Precipitation behaviour in rheocast A356 alloy is studied using ultrasonic velocity measurements. The microstructure of a given alloy has a bearing on its mechanical properties. In the present case, a study is made of the effect of solutionising and precipitation hardening on the microstructure, hardness and ultrasonic velocity (longitudinal wave velocity). During rheocasting, the melt is continuously stirred and allowed to solidify at an average cooling rate of 5 K/s. Ultrasonic C-scan imaging confirms the absence of porosity in the rheocast A356 alloy. The changes in ultrasonic velocity during the ageing treatment are due to the nucleation and growth of the precipitation process. Ageing for a very short duration at each of the ageing temperatures results in a decrease in the ultrasonic velocity when compared to the solutionised condition. In the age hardening process, the precipitates appear in the form of clusters. The nature of the distribution of these clusters contributes significantly towards variations in the bulk properties of the alloy.