MANUFACTURE OF AL-ZN-MG ALLOY HAVING SUPERIOR WELDABILITY AND RESISTANCE TO STRESS CORROSION CRACKING

摘要

PURPOSE:To obtain an Al-Zn-Mg alloy having superior weldability and resistance to stress corrosion cracking by specifying the composition of an Al-Zn-Mg alloy and conditions during the treatment and working of the alloy. CONSTITUTION:An Al alloy consisting of, by weight, 3.0-8.0% Zn, 0.3-3.0% Mg, 0.005-0.20% Ti, 0.0005-0.05% B, 0.5-1.5% Ni, one or more among 0.03-0.5% Cu, 0.03-0.5% Ag and 0.2-0.7% Si, one or more among 0.05-0.40% Mn, 0.05-0.40% Cr and 0.05-0.25% Zr, and the balance Al is melted and cast. The grain size of the resulting ingot is reduced to =1,500mum, and the ingot is homogenized at 400-550 deg.C and hot worked at 350-500 deg.C and =60% reduction of area. It is then subjected to final heat treatment so as to adjust the ratio between the minor and major axis sizes of the grains to 1:=5 and the minor axis size to =80mum.