Effect of post-welding heat treatments on mechanical properties of double lap FSW joints in high strength aluminium alloys

Abstract

The present study focuses on the effect of postwelding
heat treatments on mechanical
properties of double-lap Friction Stir Welded
(FSW) joints in 2024T3 and 7075T6
aluminium alloys. Heat treatments were
performed at aging and solution
temperatures. Micro-hardness profiles
measured on transversal sections of postwelded
heat treated joints reveal conditions
(temperature and time) of hardness
homogeneity at top, bottom and central
nugget zone along the whole measured
profile. When hardness homogeneity is
reached, fracture occurs in the nugget. The
double lap FSW joints after post-welding heat
treatments at low temperatures (200° and
300°C) have tensile properties comparable
with the as-FSW joint and fracture occurs in
7075T6 Base Material. At higher
temperatures, fracture strain is almost 50% of
joints deformed after heat treatment at lower
temperature and failure occurs inside the stir
zone. Polarized Optical Microscopy (POM)
and Scanning Electron Microscopy (SEM)
analysis reveal a progressive change in grain
size and morphology in high temperature
post-welding heat treated joints, leading to
Abnormal Grain Growth in the stir zone.