INFLUENCE OF A LOW TEMPERATURE AGEING ON THE PROPERTIES OF AL-6.5%SI-0.35%MG ALLOY
The effect of a low temperature ageing treatment on the hardness, tensile and corrosion characteristics of sand cast Al-6.5%Si-0.35%Mg alloy was studied. The temper conditions are low temperature ageing at 90oC, 95oC, 100oCand 105oC respectively followed by ageing to 180oC for 2 hrs. This was compared with the control sample which was aged directly to 180oC for 2hrs. The hardness of the Al-6.5%Si-0.35%Mg alloy was measured using the Rockwell-HRB scale hardness tester, while the tensile characteristic was evaluated using a graphical tensometer. The corrosion resistance of the alloy was evaluated using weight loss analysis in simulated sea water environment. An increase in the hardness characteristic was observed in the low temperature ageing at 90oC (7.8 HRB) as compared with (6.0 HRB) that was obtained for the control. From the tensile results obtained, the extension value for the control samples was (1.4 mm) while the sample with a low temperature ageing of 105oC gave the highest extension of (2.26 mm). Remarkable decrease in corrosion rate was observed at 95oC (2.3373 mm/yr x10-7) as compared with the control of (5.2049 mm/yr x10-7). From the Optical Microscope (OPM) and Scanning electron microscope (SEM) results, it was observed that the microstructures were refined for low temperature ageing when compared with the control samples. From these results, it can be deduced that the low temperature ageing treatment had an appreciable influence on the properties of this alloy.