Enhanced corrosion performance of magnesium phosphate conversion coating on AZ31 magnesium alloy
(1. Korea Institute of Materials Science, Gyeongnam 51508, Korea;
2. Department of Mechanical Engineering, National University of Singapore 119260, Singapore;
3. Korea University of Science and Technology, Daejeon 34113, Korea)
2. Department of Mechanical Engineering, National University of Singapore 119260, Singapore;
3. Korea University of Science and Technology, Daejeon 34113, Korea)
Abstract: Magnesium phosphate conversion coating (MPCC) was fabricated on AZ31 magnesium alloy for corrosion protection by immersion treatment in a simple MPCC solution containing Mg2+ and ions. The MPCC on AZ31 Mg alloy showed micro-cracks structure and a uniform thickness with the thickness of about 2.5 μm after 20 min of phosphating treatment. The composition analyzed by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the coating consisted of magnesium phosphate and magnesium hydroxide/oxide compounds. The MPCC showed a significant protective effect on AZ31 Mg alloy. The corrosion current of MPCC was reduced to about 3% of that of the uncoated surface and the time for the deterioration process during immersion in 0.5 mol/L NaCl solution improved from about 10 min to about 24 h.
Key words: magnesium alloy; AZ31 alloy; magnesium phosphate; conversion coating; corrosion protection