The Processing Techniques And Structure And Properties Of Aluminum Matrix Composite Tubes Partially Reinforced With TiAlSi Particles Fabricated By Centrifugal Casting

Al-Si alloys have excellent casting properties， after being modified andheat-treated, they will have good mechanical properties and processing performance, sothey are considered as a kind of promising materials for cylinder liners of engines.At the early stage of our research, semi-finished cylinder liners reinforced by SiCparticles or primary Si particles alone, or both by primary Si and Mg2Si particles havebeen developed by centrifugal casting. However, there are still some problems to besolved. Si, and Mg2Si particles have low densities (ρSi=2.33g/cm~3, ρMg2Si=1.88g/cm~3,ρAl=2.4-2.7g/cm~3), which are similar as to those of slag and pores in the aluminum alloymelt, so they will move to the same direction in centrifugal field according to Stoker’slaw, which will lead to some oxide slag and porosities existing in the particlessegregation zone, which can decrease the performance of castings.While TiAlSi intermetallic compound has a high density (ρTiAlSi≈3.1g/cm~3), highhardness, good wear resistance and thermal stability. So Ti can be added into the Al-Sialloy melt to create TiAlSi intermetallic compound, not only has the alloy good castingproperties, but the role of TiAlSi intermetallic compound has been fully played. Tubespartially reinforced by TiAlSi particles in the outer layer can be produced by centrifugalcasting, then the inner layer with oxide slag and porosities defects can be removed, anda new route of cylinder liners comes into being.In this paper, tubes respectively made of Al-12Si-7Ti and Al-16Si-7Ti alloys havebeen manufactured by centrifugal casting. And it indicates that tubes made ofAl-12Si-7Ti alloy consist of two layers, namely, the outer layer with a lot of TiAlSiparticles and the inner layer without particles. While tubes made of Al-16Si-7Ti alloyconsist of three layers, which respectively are the outer layer containing many TiAlSiparticles, the middle layer with eutectic Al-Si and α-Al, the inner layer containing anumber of primary Si particles. Organizational observations suggest that there lie nooxide slag and porosity defects in the TiAlSi particle segregation zone. What is more,the performance of TiAlSi segregation zone is better than that of melt matrix zone.In terms of segregation of TiAlSi particles, the mould temperature, the slurrytemperature and the wall thickness of tubes have been studied, and results show that thesuitable technique of Al-Si-Ti alloy tubes made by centrifugal casting is a mouldtemperature of280℃, a slurry temperature of900℃and a wall thickness of about13.3 mm, a rotation speed of3000rpm.After heat treatment, the appearance of TiAlSi almost does not change, whileprimary Si particles become rounded, and the appearance of eutectic Al-Si changes fromaborization to globular shape dispersing in the metal matrix. The hardness test resultindicates that tubes in aging state have the highest hardness values, and those in as-casthave the lowest ones. And the effect on metal matrix zone is more obvious than that onTiAlSi segregation zone.