Double compound modification was carried out for hypereutectic Al-24Si alloy. The experiment showed that double modification with phosphorus and rare earth can fine the structure of alloy. The complex modifications of phosphorus and rare earth make the coarse block primary silicon obviously refined and the large needle eutectic silicon modified to the fine fibrous or lamella ones. Phosphorus mainly refines the primary silicon. Rare earth can well refine the primary and eutectic silicon, but its modification effect on the eutectic silicon is more obvious. The alloys with the additions of 0.10% phosphorus and 0.9% rare earth have the optimal microstructure. Compared with the unmodified alloy, the primary silicon of alloys can be refined from 93.5 μm to 24.1 μm and the eutectic silicon can be refined from 8.5 μm to 5.3 μm. Mechanism of double compound modification with phosphorus and rare earth is discussed as well.
Two kinds of ZL108 alloys containing titanium are produced with electrolytic low-titanium aluminum alloy (named as ZL108D) and pure aluminum as well as Al-Ti master alloy (named as ZL108R) respectively. The influence of different titanium alloying methods on the microstructure and wear behavior is investigated. The result shows that it is an effective for grain refining of ZL108 alloy by adding titanium to the melt before casting. Addition of titanium can improve the wear resistance of ZL108 alloy, while ZL108D is superior to ZL108R. It is attributed to the addition with electrolytic low-titanium aluminum alloy results in better grain refinement.
The microstructure and wear resistance of in-situ Mg2Si/Al-Si were studied in the different content of Sb. The result shows that when the content of Sb is 0.4%, the refining effect of primary Mg2Si granules in Mg2Si/Al-Si composite is best. The shape of Mg2Si turned into fine and even granules compared to the shape of Chinese character or treelike crystal before modification. At the same, the composite shows the best wear resistance and the loss of wear quality was reduced by 19%~37%. The improvement of the wear resistance by alloy elements is related to the modification of the Mg2Si granules and enhancement of the matrix. The main wear mechanism of in-situ Mg2Si/Al-Si composite is grain-abrasion.
The influences of RE and P complex modifications on microstructures and wear-resistance of hypereutectic Al-24Si alloy were studied. The results show that the complex modifications of P and RE make the coarse block primary crystal silicon refined and their edges and angles are passivated, the large needle-like network eutectic silicon be modified to the fine lamella or particle ones. The optimum modification effect occurs with 0.10%P and 0.9%RE. The complex modification of P and RE can also obviously improve wear resistance of hypereutectic Al-24Si alloy. When the tested alloys modified with 0.10%P and 0.9%RE, the optimal wear resistance of modified alloys is obtained. The weight loss is decreased to 3.9mg from 5.4mg of the unmodified alloy, decreased by 27.8%. The abrasive wear caused by the breaking of Si phase is dominant wear mechanism of the alloy. It can be attributed to the refinement of primary silicon and eutectic silicon particles and the increase of strength and ductibility of alloys caused by the complex modification of P and RE.
Adopting quartz plate filter of 20 mesh to filter the ZL102 alloy compounded by Al-30Si coarse alloy produced by electric warming, the Fe content in the alloy is reduced to 0.43% from 1.14%, the big massive and petaloid Fe phase becomes fine block-like. The tensile strength and elongation of the alloy arrive at 182MPa and 4.3% respectively, which increased by 38% and 290% separately compared with the alloy without filtration. The mechanical property of this alloy has been close to the alloy compounded by pure Al and it can fully meet the demand of commercial production.
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