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

摘要

A surface 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 deg C and 530 deg 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 ofAl_3Ni_2 and Al_3Ni intermetallic phases . The tribological test on A17075 alloy against a hard Cr coated steel cylinder in air showed an average coefficient of friction mu 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.