Aluminum And Rare Earth Elements On The Corrosion Behavior Of Magnesium Alloys In Nacl Solution

The influence of aluminum and rare earth elements on the corrosion resistance of magnesium alloys in sodium chloride solution was investigated by using weight-loss tests, various electrochemical techniques, and various surface analysis techniques. The results of weight-loss tests of many magnesium alloys containing different concentration Al and Rare earth elements showed that the effect by only adding aluminum to improve the corrosion resistance of magnesium alloys in sodium chloride solution was unstable. However, 0.5-1.5% RE additions in magnesium-aluminum alloys are very effective. The Mg-8A1-l .5RE alloy has optimum corrosion resistance in sodium chloride solution. Furthermore, the heat treatment and quick solidification are obviously beneficial for reducing corrosion rates of Mg-Al alloys. The results of the linear polarization measurement of cast magnesium alloys in 3 .Swt% sodium chloride solution indicated that the corrosion current of Mg-8A1-l .5RE alloy is the least. Also, the potentiodynamic polarization tests indicated that the corrosion potential of Mg-8A1- 1 .5RE was more noble than pure magnesium. These comparison of the electrochemical properties of magnesium alloys proved that the addition of Al and rare earth elements was effective for improving the corrosion resistance of magnesium alloys. In order to investigate the mechanism of the influence of magnesium alloys by adding aluminum and rare earth elements, the microstructure of pure magnesium, Mg-Al and Mg-Al-RE alloys and the morphology and structure of the corrosion product film on alloys?surface in the sodium chloride solution was examined by the various surface analysis techniques including EMPA, EDS, SEM, TEM, XRD, AES etc. The results indicated that the elemental aluminum is conducive to the corrosion resistance of alloys, but its beneficial effect is limited and unstable. The RE addition can obviously increase the Al concentration in corrosion product film. and the distribution of Al in corrosion product film of Mg-Al-RE alloys was broaden due to the addition of RE. Moreover, a kind of intermetallic compound containing rich aluminum, rare earth, magnesium elements deposited along grain boundary act as poor cathode. It Indicated that the RE element promoted the formation of protective film containing elemental Al. In summary, the synergetic effect of elemental Al, RE and Mn is most important factor for improving the corrosion resistance of magnesium alloys.