Surface hardening of Al 7075 alloy by diffusion treatments of electrolytic Ni coatings

Abstract

Asurface hardening process based on Ni coating and subsequent diffusion heat treatments was studied
for Al7075 alloy. Nickel coatings with different thickness on 7075 Al alloy were obtained by electrolytic
and electroless processes . Heat treatments in inert atmosphere at 500 °C and 530 °C for different times
were performed in order to obtain surface hardening of the aluminum alloy by diffusion of Ni into the
substrate. The effect of temperature and time on the depth of hardening was studied by SEM, EDS, Glow
discharge optical spectrometry, microhardness tests and tribological tests.
Surface hardness higher than 1000 HV and depth of hardening higher than 100 mm were achieved by
diffusion of Ni layers and formation of Al3Ni2 and Al3Ni intermetallic phases .
The tribological test on Al7075 alloy against a hard Cr coated steel cylinder in air showed an average
coefficient of friction ? of about 0.5 with a wide variation range, while all the coated and treated samples
exhibited a coefficient friction of about 0.7. However, the wear scar depth of the hardened alloy is about
30 times lower than that of the Al 7075 alloy.