Dehong Lu

The Mechanical Properties of Al-30Si Alloy by Friction Stir Processing

Friction stir processing (FSP) was applied to modify the surface of a hypereutectic alloy Al-30wt.%Si, the influence of FSP passes on the size and morphology of Si particles, the mechanical properties of the materials in the stir zone was investigated. In the nugget by FSP, the silicon particles were intensely refined to several micrometers and spheroidized, and the refinement and spheroidization degree increased with FSP passes. The tensile behavior of the alloy by FSP has typically plastic feature. With FSP passes increasing, the tensile strength and the elongation increased gradually, and the improvement ratio of the elongation is more obvious. The improvement is attributed to the spheroidization and refinement of silicon particles by FSP.

Effect of cooling slope and manganese on the microstructure of hypereutectic Al-Si alloy with 2 %Fe

The effect of cooling slope (CS) on the microstructure of hypereutectic Al-22Si-2Fe (% w/w) alloys with 0%, 0.99%, and 1.36% Mn were studied. The results showed that primary Si particles (PSPs), needle-like Fe phases, coarse fishbone-shaped α-Al 15 (Fe, Mn) 3 Si 2 phases, and eutectic Si could be refined. With such a CS process, the intermetallic compounds in the alloys with different Mn/Fe ratios were examined with an optical microscope, scanning electron microscope, and X-ray diffraction. Moreover, the acicular δ-Al 4 (Fe, Mn)Si 2 and blocky α-Al 15 (Fe, Mn) 3 Si 2 phases were analyzed by transmission electron microscopy.

Microstructures and Properties of a Bainite and Martensite Dual-Phase Cast Steel Fabricated by Combination of Alloying and Controlled Cooling Heat Treatment

A bainite/martensite dual-phase cast steel was fabricated by a process of combination of alloying with Si and Mn elements and controlled cooling heat-treatment. Its microstructure was consisted of fine lower bainite with carbide particles precipitated homogeneously, martensite and a little residual austenite. Because of the good match of hardness and impact toughness, its impact wear performance was a little better than that of the isothermal quenching steel, and much better than that of high manganese steel such as Mn13.

Effect of Rolling-Remelting SIMA Process on Semi-Solid Microstructure of ZCuSn10 Alloy

Semi-solid billet of ZCuSn10 (Wt%: 88.25Cu, 10.48Sn) alloy is prepared by strain induced melt activated (SIMA) method which including rolling and remelting process. Firstly, ZCuSn10 alloy is casted, and rolling samples are cut from ingot casting. Secondly, the rolling samples are two pass or four pass rolled after holding 15 minutes at 450°C, then samples with 10% and 20% pre-deformation degree are obtained. The remelting samples are cut from pre-deformed samples. Lastly, the remelting samples are reheated up to 850°C or 875°C, water quenching after holding for 15 minutes. Then semi-solid microstructure of ZCuSn10 alloy is prepared. The semi-solid microstructure of ZCuSn10 alloy is observed and compared with annealed microstructure and microstructure of ZCuSn10 alloy directly remelted after casting. The results indicate that semi-solid microstructure of ZCuSn10 alloy by rolling-remelting SIMA process is uniform and fine grain, and spheroidization level of solid particle is well. The optimum semi-solid microstructure is obtained when alloy with pre-deformation 20% is remelted at 875°C for 15 minutes, the average grain diameter is about 75.80μm, shape factor is 1.62, and volume fraction of liquid phase reaches about 17.28%. Pre-deformation process plays a crucial role in grain refinement and spheroidization during SIMA process for preparing the semi-solid ZCuSn10 alloy, as pre-deformation degree and remelting temperature increases, volume fraction of liquid phase increases, the solid particles in semi-solid microstructure are smaller and rounder. The main mechanism of SIMA process preparing semi-solid billet of ZCuSn10 alloy is that pre-deformation breaks dendrites and stores energy of deformation into alloy, and promotes dendrites fusing through remelting process. Meanwhile, liquid phase occupies sharp corners of solid particles by Sn element diffusing from liquid phase into α solid phase, so that fine and uniform and globular α solid particles are gained.

Preparation and Thermal Shock Properties of Al2O3p/40Cr Functionally Graded Composites Materials

Al2O3p/40Cr graded composite was prepared by the squeeze casting method, and the as-cast structure, hardness, thermal shock properties of the composites were preliminary tested. The results show that the microstructure is compact and the grains of the matrix is small in the composite layer. Al2O3 particles well-distributed in the 40Cr matrix in continuous trend. The Macro-interface of 40Cr substrate and composites layer transits naturally and has good continuity, moreover the micro-interface of Al2O3 particles and the matrix is dense without any cavities. While the macrohardness decreases with the Al2O3 content reduced gradually. At the 20°C~650°C condition of the cold and heat cycle, graded composites has superior thermal shock properties than uniform composite.

Fabrication of Semisolid Billets of Hypereutectic Al-Si Alloy by Severe Plastic Deformation and Remelting

This paper preliminarily explored and proved the feasibility of fabricating semisolid thixoforming billets for a hypereutectic Al-Si alloy (AlSi29Fe3) by severe plastic deformation (SPD) and semisolid remelting. In this paper, friction stir processing (FSP) was used to refine the coarse primary silicon particles and needle-shaped iron-rich phase of the hypereutectic Al-Si alloy. The results show that the semisolid thixoforming billets obtained by the above route contain fine spherical Al grains with mean size of 34m, and second-phase particles (both primary silicon and iron-rich intermetallic) of less than 10m. The microstructure is ideal non-dendritic semisolid structure. Therefore, SPD and remelting is a promising technology for the fabrication of semisolid thixoforming billets of the hypereutectic Al-Si alloy.

Effect of Melt Treatment on Fe-Rich Phase in Al–25Si–2Fe–2Mn Alloy

The Al–25Si–2Fe–2Mn alloy melt was treated by using electromagnetic stirring, cooling slope and spray deposition technologies, respectively. By using various methods including SEM, EDS, XED and TEM, the solidification microstructure of Al–25Si–2Fe–2Mn alloys and the separation behavior and crystal structure of Fe-rich phase under different treatment modes of melts were analyzed. The result showed that under the three treatment modes, the hard phases in the microstructure of Al–25Si–2Fe–2Mn were all refined at different degrees. Among them, spray deposition yielded had the best refining effect, where the primary Si with the average diameter of about 5 μm were shown as tiny particles while granular Fe-rich phases with the average diameter of about 7 μm were dispersed into the microstructure. For the microstructure treated by cooling slope, the primary Si particles and the blocky Fe-rich phase exhibited the average diameters of about 30 and 40 μm, respectively and some Fe-rich phases were centered on the primary Si particles. In comparison, the electromagnetic stirring presented the worst refining effect. The primary Si particles, mainly appeared as blocks, showed an average diameter of about 50 μm and the blocky Fe-rich phase exhibited an average diameter of about 30 μm. In addition, some Fe-rich phases were bonded with the primary Si particles to distributed in the neighbor of latter. When the two materials were regarded as a whole, the average diameter were measured to be about 100 μm. Fe-rich phases treated by using the three treatment modes of melts were all stable α-Al15(Fe,Mn)3Si2 phases, but their in the alloys undergoing different treatments shows significantly different morphologies and distributions.

Influence of Process Parameters by Enclosed Cooling Slope Channel on Microstructures of Semi-solid ZCuSn10P1 Alloy

Semi-solid ZCuSn10P1 alloy slurry was fabricated by a novel enclosed cooling slope channel (ECSC for short). The influence of process parameters on the microstructure and Tin segregation phenomenon of ZCuSn10P1 alloy semi-solid slurry was studied with optical microscope (OM), scanning electron microscope (SEM) and energy dispersive x-ray spectrum (EDS). The results showed that the primary α-Cu phase gradually evolved from the dendrite into worm-like or fine spherical crystal under chilling of ECSC and shearing of the gravitation. The finest microstructure, the equivalent diameter was 46 ± 3 μm, and its shape factor was 0.73, could be obtained under the conditions of the pouring temperature 1080 °C, 300 mm of cooling plate inclined at 45 degrees and 5 mm flow gap. The average concentration of Tin increased from 5.85% in the conventional casting to 6.46% in semi-solid slurry in primary α-Cu phase, and the average concentration of Tin decreased from 27.94% in the conventional casting to 20.59% in semi-solid slurry in liquid. The distribution of Tin element in microstructure was refined obviously and the dendrite segregation reduced.

Deformation Behavior of Semi-Solid ZCuSn10P1 Copper Alloy during Isothermal Compression

The isothermal compression tests of semi-solid ZCuSn10P1 alloy by strain induced melt activation (SIMA) process are carried out by Gleeble-1500 thermo-mechanical simulator, and the same tests are finished to samples of as-cast ZCuSn10P1 alloy. The deformation temperature respectively is 910°C, 920°C and 930°C, and the strain respectively is 0.4 and 0.6, the strain rate is 0.5s-1, 1s-1 and 10s-1. The experimental results indicate that the deformation resistance of semi-solid ZCuSn10P1 copper alloy with smaller, more uniform and rounder solid grain is about half of the as-cast ZCuSn10P1 copper alloy. The deformation resistance of ZCuSn10P1 alloy by SIMA process decreases with the deformation temperature increasing, and the deformation resistance increases with the strain rate increasing.

Influence of Friction Stir Processing on Coarsening Dynamics of Fe-Rich Phase in Semi-Solid Al-Si-Fe Alloy

The as-cast and friction stir processed (FSP) hypereutectic AlSi29Fe3 were reheated to the semi-solid state, the coarsening dynamics of the Fe-rich phase during the process of remelting were investigated by the means of quantitatively metallurgical analysis. The results indicated that the coarsening of the Fe-rich phase in semi-solid state for both microstructures followed the Lifshitz-Slyozov-Wagner (LSW) theory:. However, the coarsening exponent n of the Fe-rich phase in the as-cast microstructure was 3, in the FSP microstructure was 2. Therefore, the growth rate of the Fe-rich phase in the FSP microstructure was larger than in the as-cast microstructure. In the meantime, the morphology of the Fe-rich phase changed to short bar from granular in the FSP microstructure.