Fabrication Of In-situ Al₃Ti_p/Al Based Composites And Their Properties

Intermetallic titanium tri-aluminide (Al₃Ti) has many advantages, such as excellent high temperature strength and oxidation resistance, but its brittleness makes it difficult to be used as constructional material. However, pure aluminum and aluminum alloys also have many characteristics such as low density, nice plasticity, and outstanding specific strength and are easily to be processed, but their high temperature properties are relatively poor. If the two kinds of materials are combined to form a kind of Al₃Ti_p/Al based composite, these shortcomings will be weakened while the advantages will be exerted as possibly.In this paper, TiO₂ (or K₂TiF₆) powder (or Al-10%Ti alloy) was added into high temperature molten pure aluminum, ZL102 and Al-17Cu alloys and Al₃Ti particles were formed by in-situ reaction between the adding and molten metal matrix. Then Ak₃Ti_p/Al based composites were prepared by centrifugal casting and permanent mould casting. The effects of processing parameters on the composite's microstructure and/or the mechanical properties (hardness, tensile strength), wear resistance and corrosion resistance were studied. The results show as the followings:1. For the Al₃Ti_p/Al based graded composites produced by centrifugal casting, the microstructure and hardness presented as gradient distributions along the radial direction. Increasing the centrifuge rotate speed, Ti content and pouring temperature will enlarge the composite's microstructure gradient and hardness gradient. And the change of processing parameters also affected the morphology of Al₃Ti particles.2. For the Al₃Ti_p/Al based composites produced by permanent mould casting, their fracture appeared as brittle fracture due to the cleavage of Al₃Ti_p. In comparison with the metal matrix, tensile strength and elongation of the composites were not improved, but the hardness improved greatly. However, the composites' tensile properties at high temperatures appeared better than the ones at room temperature, so Al₃Ti_p was helpful to improve the high temperature tensile properties. With the respect composites of different matrixes (alloys), when their Ti content was same, the tensile strength of Al₃Ti_p/ZL102 was best, the elongation of Ak₃Ti_p/Al was biggest, and the hardness of Al₃Ti_p/Al-17Cu was highest.3. The main wear mechanism of the permanent mould casting Ak₃Ti_p/Al based composites were adhesion wear. Comparing with the metal matrix alloys, the wear resistance of the composites was improved greatly (about 60%). The wear resistance of the composites at high temperatures was improved more significantly, so Al₃Ti_p was more beneficial to thecomposites' high temperature wear resistance. In the composites of different matrixes (alloys), the wear resistance of Al₃Ti_p/Al-17Cu was best, Al₃Ti_p/Al wear resistance was worst, and Al₃Ti_p/ZL102 wear resistance between them.4. The electrochemical corrosion of the Al₃Ti_p/Al based composites initiated at the interfaces between the Al₃Ti particles and matrix. The electrode potential of a phase should be increased by adding Ti element into pure aluminum or aluminum alloys, and Al₃Ti_p also has good corrosion resistance, so the composites' corrosion resistance should be improved. But the formation of Al₃Ti particles increased the phase boundaries, and these accelerated the electrochemical corrosion. Due to the effects of these two factors, the corrosion resistance of 5.5%Ti Al₃Ti_p/Al composite was superior to that of the matrix at fist, but after a certain period, the corrosion resistance of composites should be inferior to the matrix. The corrosion resistances of 8.2%Ti, 9.7%Ti Al₃Ti_p/Al and Al₃Ti_p/ZL102, Al₃Ti_p/Al-17Cu were inferior to their matrixes (alloyes). The corrosion resistances of three kind composites with different matrix (alloy) were Al₃Ti_p/Al-17Cu, Al₃Ti_p/ZL102, Al₃Ti_p/Al in an order from the best to the worst.