EFFECT OF ADDITIONS OF SIC AND AL2O3 PARTICULATES ON THE MICROSTRUCTURE AND TENSILE PROPERTIES OF AL-SI-CU-MG CAST ALLOYS

The aim of the present research work was to investigate the effects of minor additions of nickel and zirconium, as well as of the micro-ceramic dispersoids of Al2O3 and SiC, on the strength of cast Al-Si-Cu-Mg aluminum alloy 354 at high temperatures. Thermal analysis experiments were conducted to better understand the principal microstructural constituents of the alloys (e.g., phases, intermetallics and precipitates) and their evolution during aging at different temperatures and times, namely 155-350 degrees C for times from 2 to 100 h. The tensile properties of the as-cast and heat-treated alloys were determined at room and high temperatures for selected alloys/conditions based on the room temperature tensile data using ASTM B-108 permanent mold test bars. The tensile test results were examined in light of the microstructural features of the corresponding alloy samples in order to better understand the main parameters involved in the strengthening of the alloy at high temperatures. The use of quality index charts was deemed as a satisfactory means of presenting the tensile test results and for assessing the effects of micro-particulate (Al2O3, SiC) additions to the base alloy, as well as evaluating the heat treatment conditions applied to the seven 354-type alloys studied in relation to said properties.