THE EFFECT OF THERMAL AGING ON THE ABRASIVE WEAR BEHAVIOR OF AGE-HARDENING 2014-A1/SIC AND 6061-A1/SIC COMPOSITES

This paper examines changes to the abrasive wear resistance of aluminium-based composites when heat-treated to different ageing conditions. The composites studied were the age-hardenable aluminium alloys 2014 Al or 6061 Al reinforced with 3 mu m or 20 mu m SiC particles. The materials were aged at temperatures between 50 degrees C and 250 degrees C, and changes to the wear resistance were measured using a pin-on-drum machine. When aged at the lowest temperatures (between similar to 50-150 degrees C), transmission electron microscopy revealed the presence of the solute clusters (e.g. GP zones) and small coherent precipitates in the aluminium alloy matrices, and these were easily sheared by mobile dislocations. Consequently, the hardness and abrasive wear resistance of these under-aged composites were measured to be relatively low. Raising the ageing temperature to similar to 200 degrees C increased the hardness and abrasion resistance of the composites to the peak-aged condition, and this was associated with the precipitation of small intermetallic compounds which were incoherent with the crystal structures of the aluminium alloy matrices. At 250 degrees C the composites were over-aged, and this resulted in a reduction in hardness and wear resistance due to the coarsening of the intermetallic precipitates. The composites containing 20 mu m SiC particles were slightly more wear resistant than those containing 3 mu m SiC.