The Study of different coated on AZ91D surface – Electroless Nickel plating, Phosphate coating, MgO/ZrO2 duplex coating and its corrosion resistance in 3.5 wt.% NaCl aqueous.

• Main Authors: Chih-Chiang Yang, 楊誌強
• Other Authors: Shiow-Kang Yen
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107NCHU5159021%22.&searchmode=basic

碩士 === 國立中興大學 === 材料科學與工程學系所 === 107 === ABSTRACT Magnesium alloys are widely used in the 3C industry because of their good room temperature mechanical properties, good die castability and good machinability. However, since the magnesium alloy after the simple die casting has poor corrosion resistance, it is necessary to carry out a protective coating on the surface. Commercially the general surface treatment of the magnesium alloy is generally performed by a phosphate film treatment or a electroless nickel plating treatment. In this study, a ceramic composite coating has been conducted on AZ91D by electrochemical depositions including Zr(OH)4 in ZrO(NO3)2 and Mg(OH)2 in Mg(NO3)2∙6H2O aqueous solutions respectively. After annealing, a MgO/ZrO2 composite coating was derived. Compared with two specimens of commercial treatments, dynamic polarization tests in 3.5 wt.% NaCl aqueous solution were conducted to evaluate the corrosion potential (Ecorr), and the corrosion current density (icorr). It is found that the corrosion potential is in the order of electroless nickel plating > phosphorus coating > AZ91D > MgO/ZrO2, and the average corrosion current density (Icorr) is in the order of AZ91D > electroless nickel plating > Phosphorus coating > MgO/ZrO2. The results show that all three surface treated specimens have a significant decrease in the average corrosion current density (Icorr) value compared with the AZ91D raw materials. Among them, MgO/ZrO2 has the most significant reduction in the corrosion current density (Icorr).