An investigation of wear and corrosion resistance properties of magnesium alloy (AZ91D) electroplated in copper and trivalent chromium plating baths

• Main Authors: Y. H. Yeh, 葉郁虎
• Other Authors: C. A. Huang
• Format: Others
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/19002280487954719146

碩士 === 長庚大學 === 機械工程學系 === 98 === Mg alloy, AZ91D, which has a two-phase structure, was successfully electroplated in an alkaline Cu-plating bath. The Cu-coated Mg alloy specimen was further electroplated in eco-friendly acidic Cu and then trivalent Cr baths to obtain an anti-wear and anti-corrosion Cr/Cu coating. Experimental results show that the wear and corrosion resistance of the Mg alloy specimen was considerably improved by trivalent Cr electrodeposition. The hardness of the as-plated Cr deposit was drastically increased by using reduction-flame heating for 0.5 s. A superior wear and corrosion resistance was obtained when a Cu-coated Mg alloy specimen was electroplated with a trivalent Cr deposit, followed by heating with reduction-flame heating for 0.5 s. The corrosion behavior of Cu-coated and Cr/Cu-coated AZ91D specimens was studied electrochemically in 0.1 M H2SO4 with different NaCl concentrations. The corrosion resistance of Cr/Cu-coated AZ91D decreased with increasing NaCl concentration in 0.1 M H2SO4 solution. After immersion in a 0.1 M H2SO4 with a NaCl-content above 3.5 wt.%, the surface of Cr/Cu-coated AZ91D suffered a few blisters. Cracks through the Cr deposit provided active pathways for corrosion of the Cu and the AZ91D substrate. Formation of blisters on the Cr/Cu-coated AZ91D surface was confirmed based on the results of an open-circuit potential test, which detected an obvious potential drop from noble to active potentials. The above-mentioned results were measured via bonding strength, hardness, wear and corrosion tests.