Y. Sakamoto et al., Mechanical properties and corrosion resistance of Al-Mg alloys with Cu added by electron beam welding, MATER T JIM, 40(6), 1999, pp. 556-563
The changes in the mechanical properties and corrosion resistance of Al-Mg
alloys with Cu added by an electron beam welding process were investigated
using the measurements of tensile tests, anodic polarization curves and imm
ersed corrosion tests of the specimens with or without modification in a di
lute HClO4 solution at 303 K. The X-ray diffraction or EDAX analysis of the
precipitates, an analysis of the scanning electron micrographs of the spec
imens and the surface of the corroded specimens were also performed.
The main results obtained are summarized as follows:
(1) The grain size of the Al(alpha) phase of the modified Al-Mg alloys decr
eased as compared with the untreated specimens, having a size below ca. 10
mu m in diameter. The Al(alpha) + Al2Cu(theta) eutectic structure precipita
tes around the grain boundary of the Al(alpha) phase, and the surface area
ratios of the eutectic structure increase with increasing Cu content in the
modified Al-Mg alloys. However, in the modified 5154 alloy, in addition to
the Al2Cu compound, the Al2CuMg compound was also detected. (2) The mechan
ical properties such as 0.2% proof stress, U.T.S. and Vickers hardness of t
he Al-Mg alloys increased due to the modification. On the contrary, the elo
ngation of all the modified specimens is reduced below ca. 5%. (3) The corr
osion resistance of the modified specimens significantly decreased with inc
reasing Cu content in the alloys. The deterioration of the corrosion resist
ance is caused by an electrochemical interaction of galvanic coupling produ
ced between the grain of the Al(alpha) phase and the eutectic structure.