Effect of Zr content on corrosion behavior and chemically-milled surface roughness of Al-Cu-Mg alloy

Abstract

Al-Cu-Mg alloys, as important aircraft skin material in the aerospace field, should have excellent corrosion resistance and lower chemically-milled surface roughness. Fortunately, we found that microalloying with Zr elements can solve the challenges. In this work, the effects of adding the Zr to Al-3.8Cu-1.2Mg alloys the microstructural evolution, intergranular corrosion (IGC), electrochemical corrosion and chemically-milled surface roughness are investigated by using OM, SEM, and TEM studies. The electrochemical measurements tests are performed using a CHI760 electrochemical testing instrument and the chemically-milled surface roughness is measured by JB-4 C precision roughness tester. The experimental results show that the Zr additions to Al-3.8Cu-1.2Mg alloy could refine grain size, improve solidification segregation, increase the spacing of grain boundary precipitation phases, enhance corrosion resistance, and optimize the chemically-milled surface roughness. It is found that with the increase of Zr content, the precipitate-free zones (PFZs) of the alloy gradually become narrower and the grain boundary precipitation phases (GBPs) are discontinuously distributed. In addition, a narrower PFZ and discontinuous GBP are beneficial to enhance the IGC resistance of the alloy. The alloy with 0.2 wt% Zr exhibits the best corrosion resistance and the lowest chemically-milled surface roughness. The finding provides a good strategy for the high corrosion resistance and superior chemically-milled surface roughness properties for applications as aircraft skin material in the aerospace field.