Grain Refinement of Zn-50Al Alloy through the Addition of Zn-Al-Ti-C Master Alloy

Abstract

In this paper, two types of Zn-Al-Ti-C master alloy with different Ti/C ratios were produced throug a two-step method, characterized by XRD and SEM, and their refinement behaviors and mechanism in Zn-50Al alloy were studied. Both of the master alloys remarkably reduced the size of α-Al grains, impeded the dendritic growth and promote the equiaxed growth of α-Al grains in Zn-50wt.%Al alloy. The master alloy containing both TiC and dditional Ti in the Zn-Al matrix was found to have higher refinement ability than that containg only TiC. The refinement effect of both master alloys was greatly enhanced as the solidification temperature of Zn-50Al melt decreases. TiC particles were observed to be located at the center of α-Al grains and act as the nucleating substrate for α-Al. The decrease of melt solidification temperature and the presence of additional Ti atoms in the Zn-50Al melt cause higher melt supercooling, which further elevate the nucleating rate of α-Al grains on TiC particles and promote the equiaxed growth of α-Al grains.

Grain Refinement of Zn-50Al Alloy through the Addition of Zn–Al-Ti-B-C Master Alloy and Melt Thermal-Rate Treatment

“…The large difference between the effects of the two master alloys clearly results from the presence of TiAl 3-x Zn x phase in Zn-45Al-5Ti-0.82B-0.23C and its absence in Zn-45Al-4Ti-1.2B-0.33C. The same phenomenon was also observed in the refinement of Zn-Al alloy through adding Zn-Al-Ti-C master alloy [8]. Fig.…”

“…2(b)-(f) clearly suggest that these particles are TiC and TiB 2 , which are added into Zn-Al alloy through Zn-Al-Ti-B-C master alloy and clearly act as the nucleating substrate for α-Al grain in the solidification process. After the master alloy is added into Zn-Al melt, TiAl 3-x Zn x in the master alloy dissolves and releases Ti solute which, probably, segregates to surfaces of TiC and TiB 2 particles and promotes the nucleating rate, thus enhancing the refinement effect [8]. b) that melt thermal-rate treatment causes remarkable refinement of α-Al grains, with most of the grains changed from complex dendrites to rose-like structure and the size greatly reduced.…”

“…The grain refinement effect of Zn-Al-Ti-B-C master alloy in Zn-50Al alloy was examined in a procedure as previously reported in ref. 8. The melt temperature of Zn-50Al alloy at which Zn-Al-Ti-B-C master alloys were added was kept at 660℃.…”

“…The addition of Al-based master alloys, e.g. Al-Ti-B, Al-Ti-C and Al-Ti, and rare earths have been commonly used to refine Zn-Al alloys [8]. However, these grain refiners are difficult to melt completely and disperse uniformly in the Zn-Al melt due to their higher melting points and lower densities than those of Zn-Al alloys.…”