Effect of local chilling on morphology of primary α（Al） in semi-solid A356 alloy

The semi-solid slurry ofA356 alloy was prepared by low superheat pouring and slightly electromagnetic stirring, in which a pure copper rod was used to produce local chilling. The effect of chilling by the rod on morphology and size of primary a（Al） in A356 was researched. The results indicate that the chilling by the rod remarkably affects the morphology and the size of primary a（Al）. Primary a（Al） with particle-like shape is distributed uniformly in A356, and there is no transient area in structure morphology. Compared with the samples prepared without the local chilling, the nucleation rate, morphology and grain size of primary a（Al） in A356 prepared by low superheat pouring and slightly electromagnetic stirring with the rod are markedly improved. Under the condition of chilling, the pouring temperature can be suitably raised to obtain primary a（Al） with particle-like shape.     

Effect of pouring temperature on semi-solid slurry of A356 Al alloy prepared by weak electromagnetic stirring

The semi-solid slurry of A356 Al alloy was manufactured by low superheat pouring and weak electromagnetic stirring. The effects of pouring temperature on the slurry manufactured by weak electromagnetic stirring were researched. The results indicate that it is feasible to manufacture the slurry with particle-like primary phases by low superheat pouring and weak electromagnetic stirring, and there is an important effect of the pouring temperature （superheat temperature） on the morphology and the size of primary α -Al in A356 Al alloy. By the action of suitable weak electromagnetic stirring, increasing pouring temperature to put low superheat pouring in practice is capable of obtaining semi-solid slurry of A356 Al alloy with particle-like primary phase. Compared with the samples made only by low superheat pouring without stirring, raising pouting temperature by 15-35℃ above the liquidus temperature under condition of weak electromagnetic stirring can ensure the same grain size and morphology of the primary phase.     

Compressive behavior of NiAl/（Cr, Mo）Hf alloy prepared by high-pressure die casting and hot isostatic pressing

The NiAl-28Cr-5.85Mo-0.15Hf alloy was prepared by high-pressure die casting （HPDC） and subsequent hot isostatic pressing（HIP）, and tested for compressible strength and fracture behavior at 300-1 373 K. The results show that the elevated temperature 0.2% compressible yield strength as well as the room-temperature compressible fracture strain of as-HIP alloy are larger than those of the same alloy prepared by directional solidification （DS）. It suggests that the fine structures with a homogeneous distribution of fine Cr （Mo） and Hf-rich phase created by high-pressure die casting lead to these improvements.     

粉末热压新型(Al63Cu25Fe12)p/Mg复合材料的研究

采用粉末热压方法,制备了新型（Al63Cu25Fe12）p/Mg复合材料,Al63Cu25Fe12准晶颗粒均匀分散在复合材料中,而且与基体金属的结合良好,反应轻微,只在颗粒的边沿部分存在约5μm的反应层.粉末热压复合过程中的较低温度限制或减缓了准晶颗粒与基体金属之间的反应,反应层的反应产物除了准晶类似相Al13Fe4外,还存在一定的MgAl2O4氧化物.与纯Mg相比,除塑性外的其它力学性能指标均有很大提高,特别是含10%准晶颗粒的复合材料,其屈服强度显著提高到193.28MPa.     

Microstructural characterization of in situ TiC/Al and TiC/Al–20Si–5Fe–3Cu–1Mg composites prepared by spray deposition

An innovative spray-deposition technique has been applied to produce in situ TiC/Al and TiC/Al–20Si–5Fe–3Cu–1Mg composites. This technique provides a new route to solve the problems of losses and agglomeration of the reinforcement particles when they are injected into the spray cone of molten droplets during spray forming process. Experimental results have shown that the presence of needle-like Al₃Ti and Al–Si–Fe compounds, which are detrimental not only to the fracture toughness, but also to the stability of the microstructure, can be eliminated completely from the final product by using a proper Ti:C molar ratio of 1:1.3 in the Ti–C–Al preforms and adding 5 wt% TiC particles to Al–20Si–5Fe–3Cu–1Mg alloy. Moreover, another major problem of coarsening of silicon particles usually encountered in the hypereutectic Al–Si alloys has also been solved by the technique. The silicon particles in the spray-deposited 5 wt% TiC/Al–20Si–5Fe–3Cu–1Mg composite were much refined (∼2 μm) compared to those (∼5 μm) obtained in the matrix alloy without TiC addition. The formation and elimination mechanisms of Al₃Ti phase in TiC/Al composites can be explained based on thermodynamic theory. The modification of the microstructures in the spray-deposited Al–20Si–5Fe–3Cu–1Mg alloy can be interpreted in the light of the knowledge of atomic diffusion. The experimental results also showed that the ultimate tensile strength of the TiC/Al composites was improved over that of the unreinforced Al matrix.     

熔体反应制备Al3Zr（p）、Al2O3（p）／A356复合材料的凝固组织和性能

对Al-ZrOCl2体系采用熔体反应制备Al3Zr(p)、Al2O3(p)/A356复合材料。结果表明,原位生成的Al3Zr和Al2O3均为多面体位粒,且Al3Zr表面存在生长小面（facet)。复合材料凝固组织中ZrOCl2加入量的增加,颗粒分数增大,颗粒分布更均匀。但反应温度高于900℃时,Al3Zr颗粒出现板块状集聚生长,拉伸试验表明,Al3Zr(p)、Al2O3(p)／A356复合材料具有比基体更高的抗拉强度,并随ZrOCl2加入量的增加而提高,其拉伸断口为混合型断裂。