Development and Determination of the Age Hardening Characteristics of Al-2.00Mg-2.66Si Wrought Alloy

Abstract

The study, was carried out by developing the alloy using the foundry route of melting, alloying, and casting. The produced test samples were machined to produce test specimens which were subjected to precipitation hardening treatment. The test specimens were for impact and hardness test to inference the response of the developed alloy to age hardening treatment. The ageing temperature was 190 o C, and the ageing time was from 1-5 hrs. The control specimen was not age hardened and when compared with the age hardened specimens, the tested mechanical properties of the age hardened specimens were better than the control specimen. The hardness was seen to increase, with ageing time peaking at 3hrs of ageing to a value of 38.34 HRB, dropped and rose after 4hrs of ageing and continued to increase, thereby prompting curiosity. The toughness had a steady increase as the ageing time was increased, which clearly showed that the developed alloy responded to age hardening treatment. Introduction. A lot of aluminium–based alloys have been developed and characterized as can be seen in B.S. Aerospace Series, section L (aluminium and light alloys). Specification of the aluminium-based alloys is clearly stated unfortunately the specification for this research work could not be sighted however, close compositions were seen. According to the wrought aluminum alloy designation system, alloys of these series (Al-Si-Mg) are designated 6xxx. Aluminum – Magnesium – Silicon alloys are heat treatable [2, 5, 11]. Solution treatment followed by either artificial or natural ageing allows considerable increase in yield-strength (3-5 times). Ductility of the alloy decreases as a result of the heat treatment. Hardening of the alloys from this group is achieved due to precipitation of the phase Mg-Si occurring during ageing [5]. The phase has a fixed ratio between the elements content (valence compound), therefore amount of magnesium and silicon in 6xxx alloys is balance according to this ratio or with an excess of silicon. Alloys of this series possess high mechanical strength combined with good formability and corrosion resistance. Excess of silicon enhances effect of precipitation of the alloys but decreases their ductility because of segregation of silicon in the regions of grain boundaries. This adverse effect of silicon may be diminished by addition of chromium and manganese depressing recrystalization during solution treatment. Temperature of artificial ageing of 6xxx alloys is 320 – 360 o F (160 – 182 o