Effect of the Additional Element on the Weldability of High-Strength Al-Zn-Mg Alloy
Abstract:With a view to developing the high-strength Al-Zn-Mg alloy for weld structure, the weld cracking sensitivity and the stress corrosion susceptibility has been investigated using the samples containing 1-2% Mg, 4-7% Zn , 0.1-0.6%Cu and 0.2-0.6% Ag. The additional elements of Mn, Cr and Zr were slightly added, and the weld cracking sensitivity was investigated to study the improvement of weldability. The results revealed that each element improved the weld cracking sensitivity, and particularly the improved effect proved to be remarkable with the addition of Zr. The reason is considered to be the grain size at the weld metal becoming finer due to the addition of Zr, causing the tensile stress exerted on the grain boundary at the time of solidification shrinkage to be dispersed and reduced. Various welded joints were produced by using the samples containing the chemical composition of final selection, and were subjected to the investigation of mechanical properties. The results have revealed that compared with the conventional weld metal of JIS7NO1, the proof stress of the newly developed alloy was found to be approximately 40% higher in the base metal, and approximately 30% higher in the weld metal. Key Words:Al-Zn-Mg alloy, High strength, Stress corrosion cracking, Weldability