Effects Of La And Nano-SiC_p On Microstructure And Properties Of Mg₂Si/Al-Cu Composites

The reinforcing phase of Mg₂Si as in a composite material has the advantages of low density,high specific modulus,low cost,and simple preparation.However,the Mg₂Si phase in the aluminum matrix composites is generally coarse,and thus leads to poor properties to these composites.Accordingly,the poor properties restrict the material application in much field.So it is an important topic to modify the morphology of reinforced phase,size and distribution as well as enhancing the properties.In this paper,10%Mg₂Si/Al-Cu composites were prepared by melting-casting method.The effects of different content of La,different processes and different content of nano-SiC_p particles on the microstructure and mechanical properties of the composites were investigated.Firstly,the 10%Mg₂Si/Al-5Cu composites were prepared by melting-casting method.The influence of La addition on the microstructure and properties of 10%Mg₂Si/Al-Cu-xLa?x=0,0.2,0.4,0.8 wt.%?composites was investigated.The results identify the eutectic Mg₂Si phase was remarkably refined in the 10%Mg₂Si/Al-Cu composites with the addition of La,which changed from a coarse Chinese character to a small strip or dot,and the mechanical properties was improved.However,when the content of La reached 0.8wt.%,a bulky and needle-like La-rich phases was discovered.These La-rich phases affect the mechanical properties of the material.This results in a decrease in the tensile strength and elongation of the composite.Then,the influence of different processes?ultrasonic treatment and squeeze casting?on the microstructure and properties of 10%Mg₂Si/Al-Cu-0.8La composites was investigated.The experiments showed that ultrasonic treatment and squeeze casting could significantly refine eutectic Mg₂Si and La-rich phases,leading to the increase in mechanical properties.The optimal microstructure and properties were obtained in 10wt.%Mg₂Si/Al-Cu-0.8%La composites prepared by the squeeze casting assisted with ultrasonic treatment,its hardness,tensile strength and elongation are 146HV,336MPa and 2.5%respectively,which are 25.8%?26.8%and 150%higher than that of the composite without any treatment.Lastly,nano-SiC_p and Mg₂Si hybrid reinforced aluminum matrix composites were fabricated by the external addition method and melting-casting method.The influence of nano-SiC_p?0wt.%,1wt.%,and 2wt.%?addition on the microstructure and properties of 10%Mg₂Si/Al-Cu composites was investigated.The nano-SiC_p could act as good heterogeneous nuclei of eutectic Mg₂Si due to the coherent lattice relationship between nano-SiC_p and Mg₂Si.Thus,coarse eutectic Mg₂Si could be refined with the addition of nano-SiC_p.With 2%nano-SiC_p addition,coarse and flake-like eutectic Mg₂Si in 10%Mg₂Si/Al-Cu no longer existed,but serious agglomeration occured at the grain boundaries.The mechanical properties increased with the increasing nano-SiC_p content and reached peak value when 1%nano-SiC_p was added.The tensile strength and elongation were 336MPa and 3.0%,respectively,compared with 10%Mg₂Si/Al-Cu increased by 26.79%and 130.76%.