A METALLOGRAPHIC STUDY OF GRAIN REFINING OF SR-MODIFIED 356 ALLOY

摘要

The grain refining influence of Ti and B in the presence of Sr was investigated in A356.2 alloy using Al-10 wt% Ti, Al-5 wt% Ti-1 wt% B, Al-2.5 wt% Ti-2.5 wt% B, Al1.7 wt% Ti-1.4 wt% B and A1-4 wt% B master alloys. Strontium modification of the A356.2 alloy was carried out using Al-10 wt% Sr master alloy and two levels of Sr: 30 ppm and 200 ppm. The occurrence of intermetallic phases resulting from Sr-Ti and/or Sr-B interactions was investigated using electron microprobe analysis and metallographic techniques. Addition of B in amounts exceeding 0.1 wt% led to the formation of particles containing predominantly B and Sr, with a composition approaching SrB6. No interaction between Sr and Ti was observed. Thus, the boron content of the alloy should be considered as one of the parameters which would affect successful grain refinement and modification of A356.2 castings. The effect of Sr/B interaction on the grain size of the A356.2 alloy samples is also presented.