Influence of Al–5Ti–1B master alloy addition on the grain size of AZ91 alloy

Abstract

The mechanical properties of castings depend on the grain size. There is evidence that titanium and boron (Al–5Ti–1B master alloy) affect the grain size of magnesium alloys. Here, the influence of the addition of 0–1 wt. % of Al–5Ti–1B master alloy on the grain size of AZ91 magnesium alloy was investigated. Melting of the alloy was performed in steel and corundum crucibles. To study the effect of cooling rate on grain size, cylindrical samples were cast in steel and fireclay molds. The Al–5Ti–1B master alloy addition did not change the phase composition of the AZ91 alloy. This study demonstrates that the addition of Al–5Ti–1B did not contribute to the grain refinement of the AZ91 alloy, but rather led to its coarsening for samples cast in both the steel and fireclay molds. Increasing the holding time after the addition of the Al–5Ti–1B master alloy from 15 to 110 minutes also did not lead to significant grain coarsening. The mechanical properties of the AZ91 alloy samples slightly improved after Al–5Ti–1B addition. Keywords: AZ91 magnesium alloy, Grain refinement, Al–5Ti–1B master alloy, Ti addition, Growth restriction factor