The corrosion and wear resistances of magnesium alloy (LZ91) electroplated with copper and followed by 1 μm-thick chromium deposits

The Mg-Li-Zn alloy, LZ91, is a potential material for industrial application owing to its high specific strength. However, the LZ91 has so high chemical reactivity that it is easily corroded in air and an aqueous environment. In this study, an eco-friendly electrodeposition method was proposed to obtain a protective Cr/Cu coating on the LZ91 substrate. That is, the LZ91 surface electroplated a Cu undercoat in an alkaline Cu-plating bath and followed by decorative 1 μm-thick Cr electroplating in a plating bath with trivalent chromium ions. After electroplating, some of the Cr/Cu-deposited specimens were heated with a reduction flame for 0.5 s to increase the hardness of Cr-deposit. The wear resistance of as-plated and flame-hardened Cr/Cu-coated LZ91 specimens was estimated with ball-on-plate wear tester by using a steel-ball counterpart. Whereas, their corrosion resistance was evaluated in a 0.1 M H₂SO₄ solution before and after wear test. Experimental results show that a Cu deposit could be uniformly electroplated on the LZ91 surface by using our proposed electroplating method. The corrosion resistance of LZ91 was markedly improved after decorative 1 μm-thick Cr electroplating. After wear test, the steel counterpart was ground obviously with either as-plated or flame-hardened Cr/Cu-coated LZ91 specimen. According to the results of electrochemical corrosion test, some parts of the Cr deposit were peeled off from worn flame-hardened Cr/Cu LZ91 surface. This reduces its corrosion resistance significantly. On the other hand, the corrosion resistance of as-plated Cr/Cu LZ91 was not changed after wear test. That is, an as-plated Cr/Cu-coated LZ91 specimen could have good corrosion and wear resistance.