Z.X. Liu

Influences of complex modification of P and RE on microstructure and mechanical properties of hypereutectic Al-20Si alloy

P and RE complex modification of hypereutectic Al-Si alloys was conducted. The influences of P, RE content on the microstructure and mechanical properties of alloys were investigated. The complex modifications of P and RE make the coarse block primary silicon obviously refined and the large needle eutectic silicon modified to the fine fibrous or lamella ones. P mainly refines the primary silicon, but excess P is unfavorable to the refinement of primary silicon. RE can well refine the primary and eutectic silicon, but its modification effect on the eutectic silicon is more obvious. P can repress the modification of RE on the eutectic silicon. The alloys with the additions of 0.08% P and 0.60% RE have the optimal microstructure and the highest mechanical properties. Compared with the unmodified alloy, the primary silicon of alloys can be refined from 66.4 μm to 23.3 μm and the eutectic silicon can be refined from 8.3 μm to 5.2 μm. The tensile strength is improved from 256 MPa to 306 MPa and the elongation is improved from 0.35% to 0.48%.

Effect of Sb on Microstructure and Mechanical Properties of Mg2Si/Al-Si Composites

The effect of Sb on the microstructure and mechanical properties of Mg2Si/Al-Si composites was investigated. The results show that Sb can improve the microstructure and mechanical properties of Mg2Si/AI-Si composites. When the content of Sb is 0.4%, the morphology of primary Mg2Si changes from dendrites to fine particles, the average size of Mg2Si particles is refined from 52 to 25μm, and the ultimate tensile strength and elongation of the composites increase from 102.1 MPa and 0.26% to 138.6 MPa and 0.36%, respectively. The strengthening mechanism can be attributed to the fine-grain strengthening. However, excessive Sb is disadvantageous to the modification of the composites.

Microstructure and properties of Al0.3CrFe1.5MnNi0.5Tix and Al0.3CrFe1.5MnNi0.5Six high-entropy alloys

In this article, the microstructure, hardness, and corrosion resistance of the Al0.3CrFe1.5MnNi0.5Tix and Al0.3CrFe1.5MnNi0.5Six (xxa0=xa00, 0.2, 0.5, 1.0) high-entropy alloys were investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), digital display Vickers hardness tester, and electrochemical technique. These alloys are mainly composed of BCC solid-solution structure. When adding high content of Ti or Si element (xxa0≥xa00.5), some intermetallic compounds are found in the microstructure, which makes the alloys have a high hardness, high brittleness, and easy cracking. While the alloys with low content of Ti or Si (xxa0=xa00.2) have a hardness of HV 420–HV 430, and its hardness increases about 14xa0% compared with that of Al0.3CrFe1.5MnNi0.5. Electrochemical results in 3.5xa0% NaCl solution show that the alloying elements Ti and Si have a negative influence on the corrosion resistance of the Al0.3CrFe1.5MnNi0.5 alloys.

Grain refining action of Ti existing in electrolytic low-titanium aluminum with Al-4B addition for superheated Al melt

Abstract The effects of superheating temperature on the grain refining efficiency of Ti existing in electrolytic low-titanium aluminum (ELTA) without and with the Al-4B addition and the Al-5Ti-1B master alloy in pure Al were comparatively investigated. The results show that the Ti existing in ELTA without Al-4B addition exhibits a certain grain refining efficiency when the melt superheating temperature is lower, but the efficiency decreases rapidly when the superheating temperature is higher. The grain refining efficiency of the Al-5Ti-1B master alloy is better than that of the Ti existing in ELTA without Al-4B addition at any superheating temperature, but it also decreases obviously with the increase of the superheating temperature. One important reason is that the TiB 2 particles coming from the Al-5Ti-1B master alloy can settle down at the bottom of the Al melt easily when the superheating temperature is increased, thus decrease the number of the potent heterogeneous nuclei retained in the Al melt. If the Al-4B master alloy is added to the ELTA melt, the grain refining efficiency of the Ti existing in ELTA can be improved significantly, and does not decrease with the increase of the superheating temperature. This perhaps provides us a possible method to suppress the effect of the superheated melt on the microstructures of aluminum..

Effects of hot pressing temperature on microstructure, hardness and corrosion resistance of Al2NbTi3V2Zr high-entropy alloy

A novel lightweight high-entropy alloy Al2NbTi3V2Zr was fabricated by vacuum hot pressing. The effects of sintering temperature (1200–1550°C) on the microstructure, hardness and corrosion resistance of the alloy were investigated. Results showed that Al2NbTi3V2Zr mainly consisted of simple cubic matrix and (Zr, Al)-based intermetallic phase (α-phase) at sintering temperatures of 1200–1350°C. Moreover, the matrix phase transformed from simple cubic to body-centred cubic phase, and (Ti, Zr, Al)-based intermetallic precipitated from the matrix at temperature of 1450°C. The fabricated Al2NbTi3V2Zr alloy had low density of 5.05–5.23u2005gu2005cm–3, high hardness of 510–728u2005HV and excellent corrosion resistance in 10u2005wt-% HNO3 solution.

Effect of Silicon on Phase Selection of Ternary Compounds during Solidification of ZA84 Magnesium Alloy

Effect of silicon on the phase selection between τ phase (Mg32(Al, Zn)49) and φ phase (Al2Mg5Zn2) in ZA84(Mg-8Zn-4Al-0.3Mn) magnesium alloy produced by steel mold cast was studied using X-ray diffractometer, scanning electron microscope and differential scanning calorimeter. The results show that with increasing Si addition in ZA84 alloy, the liquidus temperatures of the alloys and the solidification temperature ranges decrease. The ternary compound in ZA84 alloy is mainly τ phase and a little φ phase. When adding Si to ZA84 alloy, the preferential precipitation sequence of the ternary compounds changes, φ phase preferentially forms, whereas τ phase is suppressed. The solidification kinetics study of phase selection indicates that there is a critical degree of undercooling of the melt. If the undercooling exceeds the critical degree, τ phase preferentially forms while φ phase is suppressed; otherwise, φ phase preferentially forms while τ phase is suppressed.