| 摘要 |
PURPOSE:To provide excellent weldability and resistance to stress corrosion cracking to a specifically composed Al-Zn-Mg alloy by subjecting a casting ingot of the Al-Zn-Mg alloy of which the crystal grain size is made fine to a specific value or below to a homogenization treatment at a specific temp. then to hot working to a specific reduction ratio or above at a specific temp. and forming the specific crystal grains by the final heat treatment. CONSTITUTION:The casting ingot of an Al-Zn-Mg alloy is composed of the compsn. contg., by weight %, 3-8 Zn, 0.3-3 Mg, 0.005-0.2 Ti, 0.005-0.05 B and 0.1-1.5 Ni, contg. >=1 kind among 0.05-0.4 Mn, 0.05-0.4 Cr and 0.05-0.25 Zr, consisting of the balance Al and impurities and having the crystal grain size reduced to <=1,500mu. After such alloy is subjected to a homogenization treatment at 400-550 deg.C, the alloy is hot worked at >=60% reduction ratio at 350-500 deg.C. The ratio between the short diameter and long diameter of the crystal grain after the final heat treatment is made to >=(1:5) and the length of the short diameter is made to <=6mu.
|
