Ａｌ‐Ｚｎ‐Ｍｇ‐Ｃｕ‐Ｌａ系押出合金の引張強度特性と耐応力腐食割れ性に及ぼすＣｒ，ＭｎおよびＭｇ添加の影響

Abstract

Two groups of the extruded high strength Al-Zn-Mg-Cu-La system alloys, including Al-10 wt.%Zn-1 wt.%Mg-1.5 wt.%Cu-3 wt.%La with various Cr and Mn contents and Al-8 wt.%Zn-1.2 wt.%Cu-4.0 wt.%La with various Mg contents, were developed as the mechanical materials with a good stress corrosion cracking (SCC) resistance. In these alloys, the effects of the additional elements were investigated on the mechanical properties and SCC life. The main results are as follows;(1) The second phase particles which contained Zn and La were observed in the matrix, and dispersed homogeneously. The size of the particles was 5 to 10μm. For the alloys with Cr, dispersoids including Cr were also observed in the matrix. Their size was over 10μm.(2) The maximum value of 568MPa in tensile strength was observed in Al-8 wt.%Zn-1.2 wt.%Cu-4.0 wt.%La with 2.5 wt.%Mg, which was nearly equal to the commercial aluminum alloys7075-T73 and 7475-T6.(3) The excellent resistance of SCC was obtained in these alloys. Their SCC lives were over 15 times as long as that of Al-8 wt.%Zn-1 wt.%Mg master alloy. In conclusion, we developed extruded Al-high Zn-low Mg system alloys with high strength and good SCC resistance.