Study On Microstructure And Properties Of Friction Stir Processing Magnesium Matrix Composites

Magnesium and its alloys have broad application prospects due to their low density,high specific strength,high modulus of elasticity and excellent processing properties.Comparing to aluminum or iron alloys,they have insufficient tensile strength and elongation which limiting their further application.The high processing speed friction stir processing(FSP)is a novel solid phase processing,which can refine the grain of the magnesium matrix,and the reinforcement can be uniformly dispersed into the matrix by FSP.This processing provides favorable conditions to the hardness,strength,corrosion resistance and the other properties.In this paper,nano-zirconia and graphene reinforced magnesium matrix composites are prepared by FSP.Then their performance characteristics are further studied,which provide theoretical value for the industrial application of friction stir processing technology in preparing magnesium matrix composites.The composite material prepared by FSP has a relatively uniform distribution of reinforcement.The composite obtained by three passes FSP has the most uniform reinforcement distribution.And all the magnesium-based composite material prepared by FSP can achieve the density of more than 95%.After FSP,the magnesium matrix grains are significantly refined,and the average grain size of the agitation zone reaches 8.56 ?m.A large number of dislocations also occur in the stirring zone,and nano-zirconia plays a significant role in dislocation pinning;in which a large number of dislocation walls appear,which also provides condition for fine grain.The orthogonal test system is used to study the room temperature tensile properties of composites prepared by different process parameters.It is found that the processing speed is 200mm/min,the volume fraction of zirconia is 6.43%,and the processing passes is 3,the tensile strength and elongation obtained at this condition are 270.12 MPa and 19.69%,respectively.And they are increased by 15.2% and 18.5% in respective,comparing to the base material.After FSP,the average hardness values of the two composite materials are higher than the average hardness value of the base material.The composites with zirconia reinforcement volume fractions of 2.14%,4.29% and 6.18%,respectively,have an average hardness value of 23.08%,35% and 45% compared to the parent metal.To Graphene/AZ31,the hardness of the four composites obtained under different preparation conditions increased by 29.93%,29.16%,30.34% and 28.7%,respectively.The conductivity of FSP Graphene/AZ31 composite is slightly lower than that of the parent metal,but the corrosion resistance of Graphene/AZ31 composite is stronger than that of the base metal.Graphene exists as the protective film in magnesium substrate,improving the corrosion resistance.From the micro-texture analysis of the FSP Graphene/AZ31 composition,the texture of the base metal is mainly based on the base surface slip,and the preferred orientation is obvious on the {0001} crystal plane.The texture strength of the base material area is 8.54.The orientations of TMAZ+SZ and SZ area are more obvious,while the texture strength reaches 30.42 and 28.99.What is more,the texture of the HAZ zone is similar to that of the base metal,and its texture value is 14.13.