Properties of „In Situ” 7475 Alloy Matrix Composites Reinforced Al3Ti Intermetalic Compound Extruded in Semi-Solid State

Studies were conducted to improve the mechanical properties of composites based on 7475 aluminium alloy reinforced with Al₃Ti particles fabricated by the “in situ” process. The first step involved “dissolving” of titanium in the liquid aluminium alloy and fabricating in this way composite materials with different content of the reinforcing phase (15-45wt%). A relationship between the composite hardness and content of the reinforcing phase was confirmed. The second step involved the improvement of cohesion between the reinforcing particles and composite matrix. By extrusion of samples in semi-solid state, an average increase in hardness by 15-20% relative to the unextruded composite was obtained. In the third step, the fabricated composite was subjected to a heat treatment corresponding to the state T6 in 7475 alloy, which raised the hardness by about 30%. Structure examinations carried out by means of optical microscopy and scanning electron microscopies as well as the results of hardness measurements were described. They enabled estimating the effect of the content of produced Al₃Ti particles, and of the extrusion process in semi-solid state and heat treatment parameters on the composite properties. In compression test, the yield strength and compressive strength of the heat-treated composites were determined.