Lu Li

The application demand of lightweight high-quality aluminum alloy parts in automotive and aerospace fields is increasingly. In aluminum matrix composites, reinforcing particles can significantly improve the performance of the matrix. In this paper, the microstructures and mechanical properties of die-cast 4 wt%TiB₂/Al-9Si-3Cu-0.8Zn composite were systematically analyzed by x-ray diffraction, optical microscope, scanning electron microscopy, energy dispersive spectrometer, transmission electron microscopy and tensile testing. The composite was successfully fabricated from an Al-K₂TiF₆-KBF₄ system by in situ melting technique. The research results show that the average grain sizes of the α-Al phase gradually decreased with the increase of filling distance. And the TiB₂ particles were distributed around eutectic Si in irregular polyhedral morphology or nearly circular shape. Meanwhile, the crystal structures of Ti-B compound and long needle shaped nano-sized precipitated were identified and analyzed, and they were found to be TiB₂ and Al₂Cu phase, respectively. Tensile testing results show that the mechanical properties of die-cast composite clearly increase after T6 heat treatment. The yield strength, ultimate tensile strength and elongation could reach 311 MPa, 379 MPa and 2.8% respectively, with the best injection velocity (1.8 m s⁻¹). The significantly enhancement of mechanical properties of composite after T6 heat treatment was mainly due to the introduction of TiB₂ reinforcing phase and the precipitation of Al₂Cu precipitate in the aging stage. The results implied that the introduction of TiB₂ reinforced particles could improve the mechanical properties of die castings, which has an important guiding role for its practical application.

XTiB2/Al-20%Si composite is a hypereutectic Al-20Si alloy containing x wt% TiB2 sub-micron or nanometre level in situ particles. The xTiB2/Al-20%Si composites were prepared using an 11% TiB2/Al-6Si composite as the master alloy. The phases and microstructures in the composites were evaluated by use of XRD, OM, SEM, EDS, EPMA, and TEM. The microstructural evolution of the Al-20Si alloy with the addition of TiB2 particles from 1 wt% to 6 wt% was investigated. The results showed that the primary Si, α-Al phase, and eutectic Si could be refined and modified by TiB2. Meanwhile, the crystal structures of Ti-B compound enwrapped by primary Si and α-Al phase were identified and analysed and found to form a close-packed hexagonal structure. Compared with the microstructures of composites containing different amounts of TiB2, the TiB2 particles played an important role in the nucleation of primary Si and the growth of primary Si, eutectic Si, and α-Al phases, also explaining the mechanism underpinning the effect of TiB2 on the nucleation and growth of Si and α-Al phases.

In this work, an electric current pulse (ECP) of 500A was applied on a hypereutectic high chromium cast iron (HHCCI) melt before it began to solidify, and the effect of ECP on primary carbides was investigated. The characteristics of the primary carbides were analyzed by X-ray diffraction (XRD), electron probe micro-analyzer (EPMA), transmission electron microscopy (TEM), micro hardness tester, and other techniques. The results showed that ECP not only refined the primary (Cr, Fe)₇C₃ carbides, but also decreased the average content of Cr in the primary carbides. At the same time, the average value of micro hardness of the primary carbides increased by about 84 Kgf/mm², which contradicts existing knowledge that hardness increases with an increase in Cr content. XRD analysis showed that the crystal structure of the primary carbides did not change. The results of EPMA indicated that the Cr/Fe ratio gradually decreased from the center to the edges of the carbide particles. Further investigation revealed that the uneven distribution of elements caused by ECP led to an increase in defects (including twins, antiphase boundaries, and dislocations). This increase in defect density is the main reason for the increase in micro hardness instead of the expected decrease. The mechanism of the change in primary carbides was analyzed in detail in this paper, which has provided a new method for the refinement of primary carbides and for improving the properties of primary carbides.

Three different compositions of high-Si Al alloy pipe, with a gradient structure, were produced through semi-solid rheological squeeze casting, the microstructural characteristics of which were investigated. The mechanism of gradient structure formation and the effect of acicular Fe-rich phases on liquid segregation were revealed. Meanwhile, the crystal structures of the Al₄FeSi₂ and Al₁₅(Fe, Mn)₃Si₂ phase were elucidated. The relationship between the volume fraction of hard particles in the pipe wall and the macro-hardness was established. Wear resistance tests of the inner surfaces of the pipe walls, and tensile strength tests at different positions around the pipe walls, showed that the δ-Al₄FeSi₂ phase (acicular Fe-rich phases) reduced the wear resistance and the tensile strength of the alloy. In this study, the gradient distribution of the hard particles caused the outside of the pipe wall to have a higher tensile strength.

In this paper, the CuSn10P1 alloy controlled by melt cooling stage was carried out through the enclose cooling slope channel (ECSC for short) and similar isothermal collection of crucible, meanwhile the microstructure element distribution of CuSn10P1 alloy were studied. The result shows that the liquid metal quickly cools down to the solid-liquid temperature range under the chilling effect of slit cooling channel. The primary phase rapid nucleation and growth, the distribution characteristic of the tin mass fraction of the core is lower and the outer ring is higher. The preheating crucible was used to collect the slurry which prepared by the ECSC, the latent heat of crystallization and volume temperature effect were used to carry out short-time similar isothermal treatment. With the process of similar isothermal treatment, the primary phase is aged and changes to the spherical shape, while the tin element diffuses into the primary phase from the liquid. The semi-solid slurry with the above-mentioned microstructure feature was subjected to squeeze casting to obtain shaft sleeve parts. The ultimate tensile strength and elongation of the shaft sleeve parts increased by 22% and 93%, respectively, compared with the liquid squeeze casting. This is attributed to the grain refinement and homogeneity of macroscopic concentration distribution of tin elements in CuSn10P1 alloy.

Semi-solid ZCuSn10P1 alloy slurry was fabricated by a novel enclosed cooling slope channel (ECSC). The influence of pouring length of ECSC on the microstructures of ZCuSn10P1 alloy semi-solid slurry was studied with an optical microscope an optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Liquid squeeze casting and semi-solid squeeze casting were performed under the same forming conditions, and the microstructure and properties were compared. The results show that primary α-Cu phase gradually evolved from dendrites to worm-like or equiaxed grains under the chilling action of the inner wall of the ECSC. The mass fraction of tin in the primary α-Cu phase increased from 5.85 to 6.46 after the ECSC process, and intergranular segregation was effectively suppressed. The finest microstructure can be obtained at 300 mm pouring length of ECSC; the equivalent diameter is 46.6 μm and its shape factor is 0.73. The average ultimate tensile strength and average elongation of semi-solid squeeze casting ZCuSn10P1 alloy reached 417 MPa and 12.6%, which were improved by 22% and 93%, respectively, as compared to that of liquid squeeze casting.

A gene, presumably involved in spermatogenesis, was identified and characterized by using cDNA microarray. Hybridization intensity was 2.13 fold higher in adult testis than that in fetal testis. The full length of this gene was 4288 bp and it encoded a 578 amino acid protein. Conserved structure and amino acid sequence analysis revealed that the protein contained 1 Thif-domain, 2 UBACT-domains, and a functional active site cysteine lay upstream of UBACT domain, all of them also existed in ubiquitin-activating enzyme E1 and E1 like proteins. So we named this gene as a novel ubiquitin-activating enzyme E1 like gene (nUBE1L). Expression profile showed that nUBE1L was predominantly expressed in testis. Comparison of the expression of nUBE1L in different developmental stages of testis indicated that it was highly expressed in adult testis. In conclusion, nUBE1L is a novel human E1 like gene highly expressed in adult testis, which plays key role in ubiquitin system, and accordingly influences spermatogenesis and male fertility.