Studying About Laser Cladding Al+Al₂O₃Coating At Improving The Surface Performance Of AZ91D Magnesium Alloy

Magnesium alloy has the advantages of low density、specific strength、specificstiffness、good damping and easy processing. So it has important application value andbroad application prospects in the automotive, aerospace and military field. it called"green engineering materials in the21st century", however, the hardness of magnesiumalloy is low, poor corrosion and abrasion resistance are hindered the application, in orderto solve this problem, it has important practical significance through the surfacemodification of magnesium alloy to improve its hardness, abrasion and corrosionresistance.Experiments with AZ91D magnesium alloy as the research object, using5KW flowCO2gas laser to laser cladding on the surface experiment of Al+Al2O3(the content ofAl2O3are2%、4%、6%) and improve the abrasion and corrosion resistance,usingstereoscopic microscopy (SM)、 scanning electron microscopy (SEM) and energydispersive spectrometer (EDS), X ray diffractometer for cladding microstructure, phasecomposition,composition,using micro hardness tester friction and abrasion testingmachine for micro hardness, makes analysis on abrasion performance of cladding layer,the corrosion resistance of the determination standard of weight loss method andelectrochemical corrosion method. Through the cladding layer of macroscopic andmicroscopic analysis of the cladding appropriate parameters for optimum power P=1.8Kw,scanning speed of V=7mm/s, spot diameter of D=3mm, Under the process parameters toget the surface smooth level off, the blowhole defects such as less, organization fineuniform and matrix to achieve a good metallurgical bonding.Microstructure analysis showed that the cladding layer can be divided into threeparts of the cladding area、combining area、matrix. The morphology of cladding area arecontinuous network, with different laser power and scanning speed, two kinds of Al+4% Al2O3and Al+6%Al2O3powder formed cladding mesh organization are different.Alongwith the increase of the power,mesh size become larger, part of the mesh organization intosnowflake organization. With the increase of scanning speed, mesh organization graduallybecome small. Under optimization process parameters, the combination area of Al+2%Al2O3powder cladding layer appeared small irregular shape groups. Along with theincrease of the content of Al2O3，irregular shape size increases gradually disappear.Phase analysis shows that, the cladding layer phase is mainly composed of Al2Mg、Mg17Al12、MgO、Al2O3、Al2Mg3.Hardness analysis showed that, the solution of Al2O3hard phase solid strengthening inthe coating improving the hardness of cladding layer. With the different laser processingparameters of Al+Al2O3micro hardness of coatings from matrix85HV highest increasedto340HV, which is about4times of the substrate.Abrasion test showed that, when load size remains the same, as the extension ofloading time, under different laser power, Al+Al2O3coating has the highest wearweightlessness is about a third of the AZ91D substrate.When wear and tear of time isconstant, with the increase of load size, Under different scanning speed,the Al+Al2O3coating are affected differently by load level.Corrosion experiment by weight-loss method analysis that,the corrosion rate of twokinds cladding powder of Al+2%Al2O3and Al+6%Al2O3cladding layer are lower thanthat of the AZ91D substrate. Polarization curve analysis shows that,the corrosion potentialof two kinds cladding powder of Al+2%Al2O3and Al+6%Al2O3get cladding layer arehigher than that of the AZ91D magnesium alloy substrate, the corrosion current are lowerthan the AZ91D magnesium alloy substrate. So the cladding layer corrosion resistance getincreased than the matrix.