EFFECTS OF VACUUM HOT-PRESSING PARAMETERS ON THE TENSILE PROPERTIES AND MICROSTRUCTURES OF SIC-2124 AL COMPOSITES

The effects of vacuum hot pressing temperature and pressure on tensile properties and microstructures of 20 vol.% SiC whisker (SiCw)-2124 Al composites were investigated. The tensile strength of SiCw-2124 Al composite increased rapidly with increasing vacuum hot pressing temperature up to 570 degrees C and became saturated above 570 degrees C. The increase in tensile strength with increasing vacuum hot pressing temperature is due to the enhanced densification of composite and reduced damage of whiskers from the softening of 2124 Al matrix with increasing volume fraction of liquid phase. The vacuum hot pressing pressure needed to be higher than 70 MPa to achieve densification of SiCw-2124 Al composite above 99%. A vacuum hot pressing pressure above 70 MPa was not helpful to enhance the tensile strength, since the aspect ratio of whiskers decreased owing to the damage during vacuum hot pressing. Combining the effects of the aspect ratio of whiskers and the density of composite, which are dependent on the vacuum hot pressing parameters, an equation is proposed to estimate the tensile strength of SiCw-2124 Al composite. The effect of porosity on tensile strength of SiCw-2124 Al composite was found to be more sensitive compared with powder metallurgy alloys or ceramics, since the most pores were located at whisker-matrix interfaces and reduced the load transfer efficiency between SIC whiskers and 2124 Al matrix.