Effect of casting temperature on aluminium alloy test bar properties

Abstract

After a recapitulation of the role of separately-cast test bars in checking the melt quality and the response to heat treatment, a general review is presented of the effects of pouring temperature, maximum melt temperature and prolonged holding time on the properties of aluminium sand casting alloys. Separately-cast test bars can be used successfully for melt quality evaluation only if they are cast under standardised and strictly controlled conditions. To accomplish this, they should be cast at the most suitable temperature, independently of the pouring temperature of the production castings. The aim of the present investigation was to evaluate the effect of various pouring temperatures on the mechanical properties, the grain size and the porosity (density) of separately-cast test bars in six commonly used commercial alloys. Additionally, consideration was given to the effects of overheating of the melt and of prolonged holding times at three temperature levels. The results showed that higher pouring temperatures affect markedly (although in varying degree) the properties of alloys C4, G10, 55 and SC 51, but have little or no effect on alloys SG70 and ZG61. Overheating or prolonged holding times have no lasting effect on the properties of alloys 55, SC51, SG70 and W61, provided a proper pouring temperature is used. Properties of bars from overheated alloy C4 melts could not be completely restored, and no recovery whatever could be obtained for alloy G10 melts. It is concluded that the maximum melt temperature and the pouring temperature for separately-cast test bars in alloys C4 and G10 should not exceed 720°C (1330°F), if consistent and comparable results are to be expected. For the other alloys, the use of a standardised pouring temperature (or temperature range) is essential to ensure effective melt quality control.