Research On Microstructure And Properties Of Laser Alloyed Al-SiC Layer On Magnesium Alloy

Magnesium alloys have low density(about1.8g/cm3), high specific strength andelastic modulus, good thermal conductivity, good shock absorption, organic matterand good alkali corrosion resistance, and its ability to bear impact load is greater thanaluminum. Therefore, magnesium alloy is widely used in the aerospace, missiles,transportation, electronics and other fields. It has an important application value andbroad market prospect. However, it also has some defects, such as low hardness, poorwearing and corrosion resistance，which largely restricts the further application anddevelopment in various fields. Therefore, it has great significant to use the surfacemodification treatment on magnesium alloy.In this paper, Al-SiC powder was prepared on the surface of AZ31B magnesiumalloy by laser surface alloying with the powder preset. Then the microstructure andphase composition of alloyed layer were analyzed by using SEM, XRD, EDS andother methods. And the hardness, wearing and corrosion resistance of alloyed layerwere studied. The results show that the alloying layer had good metallurgicalcombination to substrate, uniformity and dense microstructure, no pilling, no porosityand no crack under certain range of laser process parameters. XRD analysis showedthat the phase of the Al+1%SiC alloyed layer mainly consists Al3Mg2、Mg2Si、Mg17Al12、Mg2C3、Al2O3, the phase of the Al+3%SiC alloyed layer mainly consistsMg2Si、Al3Mg2、Mg17Al12、Mg2C3、Al2O3, and the phase of the Al+3%SiC alloyedlayer mainly consists Mg2Si、Al3Mg2、Mg17Al12、Al4C3、Mg2C3、Al2O3. Themicro-hardness, wear and corrosion resistance of alloyed layer were apparently higherthan the substrate. With the increased of SiC content in composite powder, thehardness of the alloy layer also increased, and the wearing resistance also got better.When the SiC content reached5%, the hardness reached the highest and wear resistance was also the best. The average hardness of alloying layer is295HV, andcompared with the magnesium alloy substrate, it raised more than four times. Thehighest hardness is336HV. At the same time, wear resistance has been greatlyimproved.The corrosion potential of AZ31B magnesium alloy substrate is-1.517V.Compared with that, the three kinds of alloyed layers’ corrosion potential respectivelyraised0.252V,0.281V and0.30V. And the corrosion current of the substrate is0.221A, the alloyed layers’ current respectively reduced0.067A,0.056A and0.056A.Compared with the substrate, the alloying layers’ corrosion resistance obviouslyenhanced.The optimal laser process parameters were obtained by many experiments. Whenthe laser power is1.8kw, scanning speed is7mm/min, the light spot diameter is3mm,the microstructure of alloying layer we got is tiny, uniform and dense, the wear andcorrosion resistance is the best.