A Study of Cu Electrodeposition Followed by Cr(III)-Based Alloy and Composite Electrodeposition on Die-Cast and Rolled Mg Alloys (AZ91, AZ61, AZ31) to Improve Their Wear and Corrosion Resistance

Until now little is known that obtaining a protective deposit on the surface of Mg alloy with electroplating in an aqueous based plating bath. The project’s applicant has developed an environment-friendly copper electroplating bath for Cu electrodeposition on the Mg alloy components and the method have been applied for Taiwan’s and USA’s patents. The working window and electroplating parameters for die-cast and rolled Mg alloys (AZ31, AZ61, and AZ91) are still not well investigated. Moreover, the binding strength and mechanism between Cu deposit and Mg alloy are not fully studied. Based on our experimental results, the Cu deposited Mg alloy specimens will be further electroplated with a protective Cr(III)-based alloy or composite deposit to increase their corrosion and wear resistance. The project will be conducted for three year. The aim in the first year is to develop an environment-friendly Cu electroplating method for as-cast and rolled Mg alloy (AZ91, AZ61 and AZ31) components. The developed electroplating bath can meet the standard requirement of operation security and wastage discharging. Moreover, the proper electroplating parameters can be determined for the Cu electrodeposition on die-cast and rolled Mg alloy specimens. In second year of the project, the copper-deposited Mg alloy (AZ 31) will be used as the substrate for further electroplating in acidic Cr(III)-based plating baths, respectively. Especially, extremely high hardness of ca. 1600 Hv can be obtained when the trivalent chromium deposit is electroplated on Mg alloys followed by annealing or induction-heating at 600oC. Therefore, it can be expected that high wear resistance of a Cr(III)/Cu deposited Mg alloy specimen can be achieved. In the last year of this project, Cr(III)-based composite electroplating will be conducted with SiC or Al2O3 nanopowder. Meanwhile, annealing and induction-heating will be done for the composite-deposited Mg alloy specimens and then their wear and corrosion resistance will be evaluated. The electroplating is conducted in an electrochemical three-electrode cell. The electroplating cell and testing specimens will be prepared by us. Moreover, annealing and induction heating will be conducted independently. The surface morphologies of deposited Mg specimens will be analyzed with atomic force microscope, surface profiler and scanning electron microscope. The microstructures of deposited Mg alloy specimens will be studied with x-ray diffractrometer, optical, scanning electron and transmission electron microscopies. The mechanical properties will be evaluated with micro-hardness test, pin-on-disc wear resistance test. The corrosion resistance of the deposited Mg alloy specimens will be measured with electrochemical three-electrode cell, in which their anodic polarization behavior in a selected solution could be studied. Based our experimental results of trivalent chromium and copper electrodeposition, a protective deposit for Mg alloy specimen will be developed without difficulty and good results can be expected. We plan publish at least two articles per year and two innovation patents after conducting this three-year project.

Project ID:PB9709-0743
External Project ID:NSC97-2221-E182-007