Synthesis And Evolution Mechanism Of Zr(Re)Pin Al Melt

The phase constitution, morphology and evolution of phosphides of Al-Zr-P and Al-RE-P master alloys were systematically studied using high scope video microscope (HSVM), field-emission scanning electron microscope (FESEM), electron probe micro-analyzer (EPMA), transmission electron microscope (TEM) and X-ray diffraction (XRD). The preparation technology of Al-Zr-P master alloy was optimized and put forward two types of the ZrP transition process of ZrP phase induced by Si. Meanwhile, the cluster structure of Al-Zr-P-Si melt was investigated. A new Al-RE-P master alloy containing REP phase was prepared and the REP was characterized. Finally, modifying and strengthening test of Al-Zr-P master alloy on Al-Si alloy and low-temperature refinement of Al-5La-1P master alloy on A390were carried out. The major research results in the present study are as follows:(1) Influence of Si on phase constitution and evolution of Al-Zr-P master alloyWhen the melt temperature is above1500℃and the mass ratio of Zr to P is above4:1, the phosphides mainly take the form of regular face-centered cubic ZrP particles. Furthermore, it is found that adding ZrP into Al-Si melts, Si atoms accumulated around ZrP phase, forming Si deficiency-layer and Si enrichment-layer. This concentration gradient of Si leads to two types of the ZrP transition process. In Si deficiency-layer, the reaction products is AlP and Zr(Al1-xSix)3. While in Si enrichment-layer, the reaction products is AlP and Zr(SixAl1-x)2. It can be confirmed by detailed investigation that the finer particles of (Al, Zr, Si) phase is Zr(Al1-xSix)3and the coarser block is Zr(SixAI1-x)2.The structure of liquid Al-Zr-P-Si alloy with varies of Si was investigated by ab initio molecular dynamics simulation. It was found that the first peaks of gZrP(r) are much higher than gAlP(r). Comparing the g(r) curves of Al-Zr-P with that of Al-Zr-P-Si, it can be found that adding Si to Al-Zr-P system lead to the variation of gZrP(r) and gAlP(r) at780℃and1800℃. From the variation of Ny and its deviation with theoretical value, it can be found that the Al atoms increased while the Zr atoms decreased surrounding P at780℃, which means the interaction force between P and Al is much higher.(2) Modification and strengthening of Al-Zr-P master alloy on Al-Si alloysThe average size of primary Si of the Al-Si multicomponent alloy can be refined to11.6μm by Al-8Zr-2P master alloy under the optimal conditions determined by using an orthogonal test, i.e., melting temperature of780℃, holding time of60min, and phosphorus addition of200ppm. Besides the solid solution strengthening effect, it is investigated that the Zr element induced by Al-8Zr-2P master alloy has an improvement on the distribution and morphology of intermetallic phases. Therefore, the σb,20℃and σb,350℃(ultimate tensile strength) of the Al-Si multicomponent alloy modified by Al-8Zr-2P master alloy can be increased by10.1%and4.4%respectively, compared with that modified by Al-3.5P master alloy.(3) Phase characterization and industrial application of Al-RE-P master alloyA new Al-RE-P master alloy with LaP, CeP and LaxCe1-xP was prepared. It can be found that the phosphides varies with the alloy composition, the phosphides were La0.25Ce0.75P, La0.42Ce0.58P, La0.5Ce0.5P, La0.58Ce0.42P and La0.75Ce0.25P corresponding to the alloy composition of Al-1La-4Ce-1P、Al-2La-3Ce-1P、Al-2.5La-2.5Ce-1P、 Al-3La-2Ce-1P and Al-4La-1Ce-1P master alloy, respectively. Meanwhile, it can be found that the a and d values of LaxCe1-xP increased with x.It can be confirmed that Si atoms can induce the transition of LaP to AlP and (Al, Si, La) phase. Detailed investigation found that the chemical composition and morphologies of the (Al, Si, La) phase were not stable, which varied with the Si content in the melts, from Al2Si2La phase with3%Si to Al5Si2.5La phase with6～18%, and the morphologies from needle-like to block and plate. The low-temperature refinement of Al-La-P master alloy on Al-Si alloy was investigated, and found that the minimum size of primary Si was19.6μm when holding60min at730℃. Therefore, the refinement of die-casting Al-Si alloys at low temperature was realized.