PRECIPITATION BEHAVIOUR IN TRACE ADDED Al-Cr ALLOYS

The effect of minor additions of zircomium and rare earths on the ageing behaviour of aluminium chromium alloy is studied and compared by microhardness measurements in samples, isothermally aged at different temperatures. A qualitative assessment of the effect of trace additions on the precipitation kinetics of the aforesaid alloys is also made on the basis of a simple corelation between the extent of age hardening and the amount of precipitation. It is observed that zircomium increases the nucleation density and thus helps to improve age hardening in aluminium chromium alloy. The rare earths on the other hand influence the growth behaviour of precipitates without increasing the nuclei density.