Flow Cessation Mechanism of β-Phase Solidification of High-Nb Tial Alloy

The spiral fluidity sample was poured by the liquid of Ti-45Al-8Nb-0.2W-0.25Cr alloy. The flow cessation mechanism of TiAl based alloys was investigated, and its model was built through the observation on the macrostructure of TiAl based alloys formed in the channel. The results showed that the morphology and size of the columnar crystal and equiaxial crystal changed a lot with the increase of flow length. The flow cessation mechanism of the alloy is the abundant growth of columnar crystal in the root, which causes to form the structure and finally give rise to the “necking” leading to flow cessation.

Microstructure of 7075 Aluminum Alloy by Homogenization

A 7075 aluminum alloy is widely used in the fields of transportation and aerospace because of its high strength and low density. In this paper, the effect of homogenization annealing on the microstructure of 7075 aluminum alloy was studied. The microstructure and second phase evolution of 7075 aluminum alloy were analyzed by optical microscope (OM), X-ray diffractometer (XRD), scanning electron microscope (SEM), energy spectrometer (EDS) and differential scanning calorimeter (DSC). The results showed that the as-cast microstructure of 7075 aluminum alloy was equiaxial crystal, and non-equilibrium eutectic microstructure Mg(Zn, Cu, Al)2 produced along the grain boundary. In the subsequent first-order homogenization annealing, part of Mg(Zn,Cu,Al)2 was converted to Al2CuMg phase. However, the transformation was not fully complete. Mg(Zn,Cu,Al)2 was then completely converted to Al2CuMg phase in the second order homogenization annealing.

Energy Absorption of Superplastic Zn-22Al Alloy Foam Manufactured through Melt Foaming Process

Closed-cell superplastic Zn-22Al alloy foams were manufactured through the melt foaming process using sodium hydrogen carbonate powder as a foaming agent. Foaming tests were carried out under different foaming temperatures, times and additive amounts of foaming agent. The porosity of Zn-22Al alloy foams were between 30 and 70%. The cell wall consisted of fine equiaxial crystal grains after solution treatment. The compressive properties of the Zn-22Al alloy foams were investigated at room temperature and high temperature. Zn-22Al alloy foams exhibited high strain rate sensitivity, which was caused by superplastic deformation of the cell wall material.

Effect of Cooling Velocity and Casting Temperature on Solidification Microstructure of Pure Al Refinement under Al-5Ti-B Alloy

The texture feature and grain refinement effect of Al-5Ti-B alloy on pure aluminum were analyzed and by adjusting the cooling velocity and casting temperature of molten aluminum,the influence of Al-5Ti-B alloy on solidification microstructure of pure aluminum was studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM) and other experimental methods. The results show that: Al-5Ti-B alloy is composed of Al, TiAl3 and TiB2. under the same solidified velocity,with the increase of the mass fraction of Al-5Ti-B alloy among the aluminum melt, solidification structure of pure aluminum equiaxed dendrite size small. But at the same additives of Al-5Ti-B alloy, the cooling rate and casting temperature have significant effects on the number and size of equiaxial crystal. Faster cooling rate and lower casting temperature of molten aluminum are favorable for the formation of thin equiaxial crystal of solidification microstructure.

The Study of Surface Longitudinal Crack on SPA-H Steel Slab by CSP

By the means of Metallographic analysis, scanning electron microscope (SEM), and energy spectrum analysis, the development of SPA-H surface middle longitudinal crack was studied. To find out the causes of the longitudinal crack, statistical method was adopted. The result shows that, the generating process of longitudinal crack was: the changing of mould powder owing to Ti and Al element, low overheating degree, and bad slag smelting, which leading to bad transfer heat of slab and depression. For the thermal stress of solidifying contraction, molten steel static pressure, and mould friction, the stress concentration was produced in the weak place of solidified shell, for example, in the small equiaxial crystal less than 1mm. the cracking occurred when the stress more than allow strength of high temperature slab.

The Influence of Solidification Condition to the Aluminum Wire Organization Characteristics

Electrical wiring is the main fireorigin on electrical fire, and aluminum wire laying lines used more fire hazard. The melting mark formed in process of fire is the important material evidence to analysis the cause, but the aluminum wire melting mark organization feature is also different in different solidification conditions, therefore, to identify the mark characteristics formaed in different environment conditions has become a important task of fire evidence identification. Prepared fire sample melting by the means of simulation test, and observed to analysis the experimental sample, then summarizes the influence of solidification environment on microstructure characteristics of aluminum wire trace sample. Through the analysis found that, because of the influence of subcooled temperature, make the most of the organization of melt mark cooled in the air have oversize equiaxial crystal organization, almost no holes; and the dip in water cooling of melting mark is formed in larger subcooling, so the organization have more than a small columnar crystal and cellular crystal, and have more small holes exist. These features of aluminum conductor mark can provide strong technical support for fire investigation.

Microstructure and Wear Behavior of Ti-Matrix Functional Gradient Layer

To improve the wear-resistance of Ti600, and alleviate thermal stress as well under hyperthermal and excessive temperature difference condition, experiments of Ti-matrix FGM on Ti600 substrate by pulsed Nd:YAG had been carried out. The microstructures, microhardness and phase composition of FGM were investigated. And the friction wear properties of FGM, N-FGM and Ti600 substrate were examined in atmosphere. It was found that a rapidly solidified microstructure consisting of in situ synthesized TiC reinforced phase distributed on FGM substance evenly and dispersely in the form of globular grains had three main different shapes:bulky or imperfect arborescent crystal, fine or approximately equiaxial crystal and chopped fibriform crystal. With the increasing of original Cr3C2content, the number and size of arborescent crystal increased obviously. The distribution of main alloy components was gradient and continuous, presenting the same composition and regularity to the originally preset alloy powder. FGM and N-FGM had an average hardness of approximately 1450, 4.5-5 times of Ti600 substrate, attributed to TiC primary dendrites. With the reducing of weight percentage of TiC, microhardness decreased gradiently and continuously. Meanwhile, the wear resistance of FGM and N-FGM was improved obviously. Friction coefficient, wear loss and wear rate decreased significantly, 0.3-0.5 times of Ti600 substrate.