| Hypereutectic Al-Si alloys with high silicon content (20%～26%Si), which show excellent comprehensive performances such as good thermal and wear resistance, low coefficient of thermal expansion (CTE), and high specific strength, etc, are considered to be ideal materials for heat-resistant and wear-resistant parts in the field of transportation and aviation. However, coarse primary Si particles commonly formed in this alloy which was produced by traditional process, leading to poor performances and difficult to be machined. Recently, in order to meet the need of service performances, the studies on preparing high silicon aluminum alloy were focused on these aspects such as addition of alloying elements, application of new modification agent and novel forming process. The problem of how to further improve the mechanical properties at high temperature and reduce the CTE of hypereutectic Al-Si alloys was mainly studied in this paper. A novel aluminum alloy material and its forming technique were developed to meet the immediate demand for the materials with good heat resistance and low CTE.A new type of aluminum alloy material with high silicon content and multi-element addition (SPR aluminum alloy for short) was developed. The preparing processes such as melting, modifying, etc, were studied and optimized. Then the effects of elements Mg, RE and their interaction on microstructure and properties of this alloy were investigated systematically. The results show that the tensile strength of SPR aluminum alloy with T6 heat treatment is improved significantly with the increase of Mg content. Moreover, more needle-like RE-containing intermetallic compounds would be promoted to form. The eutectic Si plates are modified apparently with the proper addition of RE amount. But the formation of acicular Al2Si2RE compounds caused by the excessive RE, would decrease the tensile strength significantly. Comparing and analyzing the performances of the alloys with different composition, the optimized compositions of SPR aluminum alloy as Al-20Si-2Cu-(0.4-0.6)Mg-1Ni-0.5Mn-(0.3-0.6)RE are obtained. The SPR aluminum alloy produced by the optimized complex modification process with P+RE addition, presents much more excellent properties than A390 aluminum alloy. The properties of this SPR aluminum alloy are listed as following, room temperature tensile strength is 295MPa, high temperature tensile strength at 300℃is 154MPa, the CTE in the range of 25～300℃is 17.4157×10-6(1/℃), the Brinell Hardness is 128.The preparing technique of semi-solid slurry of SPR aluminum alloy with ultrasonic vibration process was developed. The primary Si particles of high silicon aluminum alloy can be further refined to smaller than 20μm by this process, which is beneficial to improve the properties of this material. The effect of ultrasonic vibration temperature ranges on the quality of semi-solid slurry was mainly studied. The size and roundness of primary Si particles of SPR aluminum alloy samples, which were obtained by water quenching under different process conditions, were analyzed and compared. The optimized parameters for preparing semi-solid slurry of SPR aluminum alloy are presented as following that the temperature range under ultrasonic vibration is 710～690℃, the time for vibration is about 120s, the power is 1200w, and the holding temperature of sample cup is around 620℃. The slurry of SPR aluminum alloy prepared by this process, shows fine and round primary Si particles with the average grain diameter about 17μm and the average shape factor about 0.58. In addition, the refining effect of ultrasonic vibration treatment on solidified microstructure can be observed obviously by analyzing the primary Si particles and RE-containing compounds of SPR aluminum alloys formed by semi-solid slurry directly.The effects of parameters in die casting process on the filling capacity, microstructure and properties of SPR aluminum alloy rheo-casted with semi-solid slurry, were studied systematically. The optimized forming process with semi-solid die-casting was obtained. The results show that semi-solid slurry of SPR aluminum alloy prepared by ultrasonic vibration presents good filling ability with the maximum length of snake-like sample up to 2118mm. The properties of rheo-casted SPR aluminum alloy can be improved obviously through T6 heat treatment for the dense microstructure. While the traditional die casting SPR aluminum alloy is not able to experience heat treatment for the existence of many pores, which restricts the improvement of properties. Rheo-casted SPR aluminum alloy presents better properties than that of rheo-casted A390 aluminum alloy and traditional die casted SPR aluminum alloy. The room temperature and high temperature tensile strength at 300℃of rheo-casted SPR aluminum alloy are 320MPa and 167MPa respectively, the CTE value between 25～300℃is 17.3706×10-6(1/℃), and the Brinell hardness is up to 140.In order to explore a new method to improve the heat resistance and wear resistance at high temperature of aluminum alloy, the microstructure and properties of high silicon aluminum alloy with Fe addition were studied. Ultrasonic vibration treatment was introduced into the refining process of Fe-containing intermetallic compounds. The effects of the parameters of ultrasonic vibration process on the Fe-containing phases were first investigated systematically. The mechanism of changed morphologies of Fe-containing phases was also discussed. The results show that the needle-likeβ-Al5FeSi phase can be eliminated effectively by the combination of ultrasonic vibration treatment and a small amount addition of Mn, leading to the formation of Fe-containing phase in the form of fine blockδ-Al4FeSi2 phase. The acoustic cavitation and acoustic streaming generated by ultrasonic vibration have the effects of decreasing the start-freezing temperature ofβphase and promoting the formation of fine 8 phase. The Mn element plays the role of neutralization through joining in the formation of Fe-containing phases. Compared with the properties of SPR aluminum alloy, lower CTE and better wear resistance can be obtained by the high silicon aluminum alloy with Fe addition after ultrasonic vibration treatment.A typical heat-resistant and wear-resistant part—a swash plate for the air conditioning compressor of automotive—was fabricated by the combination of preparing semi-solid slurry of SPR aluminum alloy with ultrasonic vibration process and squeeze casting. The differences, in the forming mechanism of non-equilibrium a-Al phase and primary Si particles of SPR aluminum alloys, which were produced by traditional squeeze casting and semi-solid squeeze casting, were compared and discussed respectively. The rapid cooling rate is considered to be the main reason for the formation of non-equilibrium a-Al dendrites of traditional squeeze casted SPR aluminum alloy. The formation of spherical a-Al grains of semi-solid squeeze casted alloy is caused by the local high pressure and semi-solid slurry process under the ultrasonic vibration condition. The SPR aluminum alloy parts with higher density and finer microstructure can be produced by semi-solid squeeze casting.
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