Corrosion And Wear Of Al-Mg₂Si Composite Coating On Magnesium Alloy

Magnesium alloys have great potential for application in aerospace,automotive,3C military,and other fields due to their low density,high specific strength,and easy recovery and processing.However,the magnesium alloys have poor corrosion resistance,low hardness and poor wear resistance which greatly limit their more applications.In order to improve the performance of magnesium alloy surface,this paper adopts oxygen acetylene flame spraying technology to prepare Al-Mg₂Si composite coating on the surface of magnesium alloy.Phase composition,ingredient distribution and microstructure of the coating were analyzed by means of XRD,SEM and EDS.The micro-hardness of magnesium alloy,aluminum coating and Al-Mg₂Si composite coating were tested by micro-hardness tester.The corrosion resistance of magnesium alloy,aluminum coating and Al-Mg₂Si composite coating were comparatively studied by electrochemical tests.And the corrosion resistance of the Al-Mg₂Si composite coatings which were sealed,cold pressed and untreated was further compared.The corrosion rate of magnesium alloy and Al-Mg₂Si coating were studied by immersion test.The wear resistance was investigated by dry friction and wear test.And the influence of different loads and frequencies were investigated during the dry friction and wear test.The test results are as follows:?1?Al-Mg₂Si composite coating material could be prepared on AZ31B magnesium alloy matrix by flame spraying technology.The precipitated phases in the coating were Mg₂Si and Al.In addition,there were amount of Mg,Si and MgAl₂O₄.The density of the coating increased with increasing Al content.?2?Electrochemical tests showed that the corrosion potential of Al-Mg₂Si composite coating was positively shifted compared with the magnesium alloy.The corrosion potential of magnesium alloy was-1.4888 V,and the corrosion current density was 2.817×10^-3 A/cm².Compared with the AZ31B magnesium alloy,the corrosion potential of Al?20%?-Mg₂Si which had the most positive potential moved positively by 0.5288 V,Al?40%?-Mg₂Si followed,and Al?80%?-Mg₂Si coating moved least.And the corrosion current density of the coating was reduced by three orders of magnitude.In a word,the corrosion resistance of the Al?20%?-Mg₂Si composite coating was the best.?3?The micro-hardness test results showed that the micro-hardness of Al-Mg₂Si composite coating was higher than that of magnesium alloy,and with the decrease of Al content,the micro-hardness of the coating was increasing.The Al-Mg₂Si composite coating had a maximum micro-hardness of 335 HV,which was 5.9 times that of the magnesium alloy.?4?During dry friction and wear processes,the friction coefficient of the composite coating gradually decreased with the decrease of Al content.The friction coefficient of the Al?80%?-Mg₂Si composite coating was different from that of the Al?20%?-Mg₂Si coating by 0.55.The volume wear rate of the composite coating also gradually decreased with the decrease of the Al content.The volume wear rate of the Al?80%?-Mg₂Si coating was 36 times that of the Al?20%?-Mg₂Si coating.Therefore,reducing the content of Al in Al-Mg₂Si composite coating could improve its anti-friction and wear properties.?5?During the process of corrosion friction and wear,the friction coefficient of the coating gradually increased with the increase of the amount of Al added,in order of 0.78,0.95,1.05,and 1.15.The volume wear rate of the coating increased monotonously with the increase of Al content,and the highest Al content coating wear rate was 2.5 times that of the lowest content coating.?6?When the load was fixed,the friction coefficient of Al-Mg₂Si composite coating decreases with the increase of friction frequency,while the wear rate increases.When the frequency is fixed,the friction coefficient and volume wear rate of Al-Mg₂Si composite coating increase with the increase of load.The influence of corrosion fluid on the friction coefficient is mainly reflected in the conditions of constant load and variable frequency conditions.Compared with the dry friction and wear under the same working conditions,the friction coefficient under the wet friction condition is slightly lower and the volume wear rate is slightly higher.