Mg Matrix Composites Reforced With Nano Patricles Fabricad By SPS Followed By Hot Extrsion

Not only Mg matrix composites have a lot of advantages such as low density,high specific strength etc.,but also it overcomes much disadvantages of Mg alloy due to the synergistic effect between the matrix and the reinforcements.Therefore,Mg matrix composites have gained great attention.Many conventional fabrication methods have been used to produce the Mg matrix composites,such as stir casting,squeeze infiltration,powder metallurgy and so on.However,shrinkage porosities and cavities exist in the materials fabricated by casting method and the latter two methods are more complex and dangerous.Spark plasma sintering(SPS)is a new technology developed in recent years and it has the advantages of higher efficiency,more manageable and environment friendly.So in this paper,the Mg-1Al-xCNTs(x = 0.08,0.15,0.30,0.60 wt.%)composites and Mg-1Al-xSiC(x = 0.3,0.6,1.2,2.4 wt.%)composites were fabricated by SPS followed by hot extrusion.Their microstructure evolution,hardness,tensile and compressive properties were investigated.The enhancement mechanisms of Mg matrix composites were also revealed.For Mg-1Al-xCNTs composites,the results of microstructural characterization revealed that the Al-CNTs particles were distributed uniformly in Mg matrix.The results of mechanical properties indicated a fact that compared with monolithic Mg,all Mg-1Al-xCNTs composites,especially the Mg-1Al-0.15 CNTs composite,fabricated by SPS followed by hot extrusion exhibited better tensile and compressive properties.In tension,Mg-1Al-0.15 CNTs composite exhibited higher 0.2% tensile yield strength(157MPa vs.98 MPa,increased by ~60%)and ultimate tensile strength(271 MPa vs.188 MPa,increased by ~44%)than monolithic Mg.In compression,Mg-1Al-0.15 CNTs composite also obtained a great enhancement in 0.2% compressive yield strength(118 MPa vs.81 MPa,increased by ~46%)and ultimate compressive strength(321 MPa vs.255 MPa,increased by ~26%)compared to the monolithic Mg.Meanwhile,the Mg-1Al-0.15 CNTs composite produced by SPS followed by hot extrusion maintained a high tensile failure strain of ~8.8% and a high compressive failure strain of ~17.9%.The improved strength of Mg-1Al-xCNTs composites can be attributed to Hall-Petch strengthening,Orowan strengthening,the elastic modulus mismatch strengthening,the coefficient of thermal expansion mismatch strengthening and Load transfer strengthening.For Mg-1Al-xSiC composites,the results of microstructural characterization indicated that a large proportion of nano SiC particles distributed homogeniously in the Mg matrix,although some of localized agglomerates were found in the matrix.Mg-1Al-xSiC composites have a great enhancement in tensile properties and compressive properties as compared to the monolithic Mg fabricated by the same method.For example,compared to monolithic Mg,Mg-1Al-1.2SiC composite exhibited higher 0.2% tensile yield strength(176 MPa vs.98 MPa,increased by ~80%),ultimate tensile strength(246 MPa vs.188 MPa,increased by ~31%),0.2% compressive yield strength(140 MPa vs.81 MPa,increased by ~73%)and ultimate compressive strength(338 MPa vs.255 MPa,increased by ~33%)without much reduction on failure strain.Improved tensile/compressive strength of the Mg-1Al-xSiC composites can be attributed to the basic strengthening mechanisms including the mismatch in CTE,Orowan strengthening and load transfer strengthening.