Abstract
Key words
master alloy, refinement, hypereutectic aluminum alloy, primary silicon, modification, peritectic temperature.
Abstract
Phosphorus modified hyper-eutectic aluminum silicon alloys (silumins) are widely used to produce the details for high-power engine due to their outstanding characteristics. In this paper, Al-Cu-P self-made master alloy is used to refine the primary silicon crystals of hyper-eutectic silumins. It has been known that phosphorus acts as a nucleation site for the primary Si. The modification process does not need high melt temperature and long modification time. Results of this method are widely used in the aluminum production industry, especially for hyper-eutectic silumins. The raw materials used in the paper were hyper-eutectic silumins. Which compositions are as follows: Si,(16-21)wt.%; Cu,(2.69-4.01)wt.%; Ni,(0.86-1.0)wt.%; Mn up to 0.61wt.%.Phase diagram of non-alloyed and Cu, Ni, Mg alloyed silumins were built. These alloys contain 18wt. % Si and 20wt. % Si. This paper clarifies the effect of amount of Al-Cu-P master alloy on size of silicon constituent, mechanical properties, wear resistance and thermal expansion of hyper-eutectic silumins. The results showed that the AlP phase was formed. It can use to explain the refinement mechanism of hyper- eutectic silumins. In right modification conditions, size of primary silicon crystal decreased from 155 μm to 20 μm; tensile strength increased from 112 MPa to 170 MPa; expansibility is approximate 2%; hardness increased from 112 HB to 174 HB, thermal expansion decreased to 18.6×10-6 m/mK when temperature increased from 293K to 573K and, finally, wear resistance is improved.