Structure and wear resistance of Al-Cr-Cu alloy pipes produced by a semi-solid centrifugal casting process

The solidification structure, hardness and wear resistance of surface composite castings of an Al-Cr-Cu alloy produced by a two-step process of stir mix-quenching and centrifugal casting have been investigated. In this process, two kinds of molten metals with different compositions are mixed with agitation in a mixing vessel to produce semi-solid slurry containing fine intermetallic crystals, and then the slurry is centrifugally cast. In the stir-mix-quenching experiments, a hypoeutectic Al-Cu alloy melt was used for "the first melt" which acts as a coolant, and a hyperperitectic Al-Cr alloy melt with a higher liquidus temperature was used for "the second melt," which is rapidly quenched to precipitate numerous primary intermetallic crystals when it is brought into contact with the first melt. The structure, hardness and wear resistance of the specimen vary with the mass fraction of alpha-phase (aluminum solid solution) in the slurry. As the fraction of alpha-phase increases, the volume of macroscopic pores and hardness of the composite layer decrease. On the other hand, the composite layer has good wear resistance when the slurry with proper amount of alpha-phase was used. In such case, theta-phase (Al2Cu) acts as an bonding material for the primary intermetallic crystals to form rigid network of hard phases.