Effect of Mixing Condition on the Mechanical Properties of Magnesium Based Composites

Abstract

Magnesium based composites reinforced with S i c particles were fabricated by powder metallurgy method. In this study, the effects of mixing conditions, i.e; mixing speed and mixing duration on the mechanical properties of the magnesium based composites were investigated. The hardness, tensile strength and microstructure of composites were studied. It was found that increase of the mixing speed and prolong the mixing time can improved the distribution of Sic particle and mechanical properties of magnesium based composites. Experimental ProcedureA relatively coarse magnesium powders with average particle size of 180pm was used as matrix materials. Silicon carbide (Sic) particles with particle size ranging from 0.5 to 25 pm were used as a reinforcement phase, where the weight fractions were in the range of 5-15wt%. In this study, the Mg powders and Sic particulates were mixed in cylindrical container by using a rotating ball milling machine under a different rotating speed, 84 rpm and 168 rpm. The mixing time ranged from 6 to 24 hours without using any balls or process agent to avoid heat generation during mixing. The fraction of Sic was 5, 10 and 15wt%. The mixed powders were poured in the steel die and pressed at 300MPa and then sintered in the temperature 605°C with the holding time of 2 hours in vacuum. The sintered samples were 30 mm in diameter with 8 mm in thickness. Figure 4.1 shows the SEM observation of the Mg-15wt%SiC composites with mixing speed of 84 rpm. The pores could be observed in the agglomerated Sic at low mixing speed, 84 rpm. This is due to the absence of adhesion between the S i c particles in the clustered regions results in the particle falling out during sectioning and leading to visible porosity in these areas [I]. Figure 1 : the SEM observation of the Mg-1 5wt%SiC composites with mixing speed of 84 rpm Figure 2 shows the SEM observation of the Mg-Sic composites which higher mixing speed, 168 rpm. At higher mixing speed, the distribution of Sic particles was improved. This indicated that slow mixing speed prolongs the time necessary to obtain adequate mixing and faster mixing speed may improve mixing [2]. Result and Discussion