Work-hardening Behavior and Strength of an Al-Zn-Mg Alloy Weldment(II)

Abstract

Plates of an Al-Zn-Mg alloy were welded using an Al-Mg alloy filler rod-wire. The age and work hardening behavior of the welded joint was investigated by hardness test and microscopic observation. The results obtained are summarized as follows.
(1) Softened zone caused by weld-heat was about 40 mm in width. Immediately after welding, hardnesses of deposited metal and H.A.Z. were 70 and 90 V.H.N. respectively. Hardnesses of deposited metal and heat affected zone were both increased by room temperature aging. The hardening rate depended on distance from the center of weld. Hsrdness on deposited metal reached 95 VHN and, on heat affected zone, 110 VHN after 2 months aging.
(2) Age hardening rate at 80°and 110°C was great and over aging phenomena occurred rapidly.
(3) From the relationship between hardness and aging time it was found that there was remarkable difference in hardening rate between deposited metal and heat affected zone at 80°C ageing. Hardness of deposited metal was always less than that of heat affected zone at 110°C aging.
(4) Work hardening of the center of deposited metal was obtainable by working the weld-reinforcement. Hardness of deposited metal increased to the hardness as that of heat affected zone by 25% working after room temperature aging.