Study on Weldable Al-Zn-Mg Alloys. (Report 2)

Effect of additional elements on Weld-crack susceptibility

Abstract

A study has been made of the effect of additional elements on the weld-crack susceptibility of Al-4.5% Zn-1.5% Mg and Al-5.0% Zn-2.0% Mg alloys.
Weld-crack susceptibility was evaluated by MIG-spot cracking and Fish-bone cracking tests. The former was carried out with 5356 filler and the latter was carried out without filler, with Al-Zn-Mg filler, 5356 filler or parent metal filler.
The results were as follows:
1). The addition of zirconium to parent metal has a remarkable effect for reducing weld-crack susceptibility.
2). Neither titanium nor boron addition has any appreciable effect, though these elements serve as well to refine the structure of the weld metal as zirconium does. Titanium however, has some effect for reducing weld-crack susceptibility, only when 5356 filler is used.
3). None of other additional elements such as copper, silver, chromium and manganese was found to be effective for reducing weld-crack susceptibility.
4). Weld-crack susceptibility depends not only on the grain size but also on the volume and form of the liquid film, which is formed with boundary segregation of eutectic composition far from equilibrium.