Effect of scandium and titanium–boron on grain refinement and hot cracking of aluminium alloy 7108

TLDR

A circular patch test was used to assess how scandium and titanium–boron affect hot‑cracking susceptibility in welds on cast 7108 alloy coupons treated with various grain refiners. Scandium and titanium–boron additions refined grain size and reduced hot‑cracking susceptibility in welds, with scandium above 0.25 wt % eliminating cracking entirely and TiB₂ as low as 0.02 wt % Ti (0.004 wt % B) also preventing cracking; castings were more effectively refined by scandium, achieving finer grains than with TiB₂.

Abstract

The effect of scandium and titanium–boron (Tibor) additions on the solidification behaviour of castings and welds of aluminium alloy 7108 has been investigated. A circular patch test was adopted to evaluate the effects of these elements on the hot cracking suscepti bility of welds made on cast coupons treated with different grain refiner additions. It was observed that grain size, as well as cracking susceptibility, decreased with increasing amounts of scandium and that hot cracking was completely eliminated at scandium additions above 0·25 wt-%. A more pronounced grain refining effect in welds was observed with Tibor and, in addition, no hot cracking was observed with Tibor additions as low as 0·02 wt-%Ti (0·004 wt-%B). Castings, however, were more effectively grain refined with scandium, achieving a finer grain size than with Tibor.