快淬Fe-Si-Al软磁合金的扁平化、微结构与电磁性能研究

用快淬法制备Fe-Si-Al合金薄带,通过高能球磨对其进行扁平化处理,在氮气保护下进行700℃退火处理30min。研究了高能球磨工艺和退火处理对Fe-Si-Al合金样品形貌、结构及磁性能的影响。结果表明,高能球磨70h后,Fe-Si-Al合金薄带细化为纵横比较大的扁平状微粉;后续的退火处理有效提高了合金样品的饱和磁化强度;利用退火态扁平化微粉制备的同轴圆环样品,在1GHz附近具有良好的抗电磁干扰(EMI)特性。

Ti-Si-Al合金的显微组织与滑动摩擦学行为研究

研究了Al元素对Ti-Si共晶合金显微组织和滑动摩擦学行为的影响.结果表明,添加7.3%的Al改善了铸态合金的微观组织,形成了由近等轴状Ti5Si3颗粒增强α-Ti(Al,Si)固溶相的有利形态.Al的加入可同时提高合金的强度、硬度和塑性,从而有效抑制了磨损亚表层裂纹的生长,在磨损表面产生了具有保护作用的机械混合层,从而显著地提高了合金的耐磨性和摩擦稳定性.

新型电子封装Si-Al合金的基础研究

对传统金属电子封装材料的研究开发现状进行了简单评述。利用喷射沉积成形技术制备了Si-Al(含硅量 5 0～ 70wt% )合金。这种合金具有细小均匀的显微组织 ,同时具有低热膨胀系数、高热传导率和低密度等特点。

喷射成形电子封装Si-Al合金凝固过程模拟研究

为了优化喷射成形Si-Al合金成形工艺 ,获得优良的显微组织 ,本文模拟了喷射成形Si-3 0wt%Al合金的凝固过程。研究了雾化压力和沉积距离对熔滴冷却过程中的温度和固相分数的影响。模拟计算结果得到实验验证。

Mg_2Si-Al合金材料的凝固与半固态组织制备

Mg_2Si-Al合金具有较多的优点,有着广泛的应用前景。探讨了Mg_2Si-Al合金的凝固行为,研究了半固态合金的制备方法,探讨了形成机制。结果发现,Mg_2Si/Al复合材料按照如下凝固过程进行:L→L_1+Mg_2Si_p→L_2+(Al+Mg_2Si)e+Mg_2Si_p→(Al+Si+Mg_2Si)e+(Si+Mg_2Si)e+Mg2Si_p。

Mg-8Zn-4Al-1Si-0．3Mn-xAlP合金的显微组织及性能

研究了AlP对Mg2Si相及其基体组织的细化效果和机理.结果表明:AlP能够作为Mg2Si初生相的异质核心,促使其由汉字形变为颗粒状,并且促进τ(Mg32(Al,Zn)49)相的析出,而抑制ψ(Al2Mg5Zn2)相的析出,同时基体组织也得到显著细化,不仅改善了合金的室温性能,而且也改善了高温(150℃)性能.

Cu-Ni-Al-Si合金固溶-时效处理

用扫描电镜、硬度计、涡流导电率测试仪和万能试验机测试分析了固溶-时效工艺对Cu-Ni-Al-Si合金组织和性能的影响,探讨了合金的强化机理。结果表明,该合金具有显著的时效强化特性,经960℃×1.5 h固溶+480℃×3 h时效工艺处理后,抗拉强度为860.3 MPa,屈服强度为743.7 MPa,伸长率为17.6%,合金的硬度达272 HB,导电率为18.9%IACS。

Microstructure evolution and tensile behavior of balanced Al−Mg−Si alloy with various homogenization parameters

The effects of homogenization parameters on the microstructure evolution and tensile behavior of a balanced Al−Mg−Si alloy were investigated using the optical microscope,scanning electron microscope,X-ray diffraction,electron probe microanalyzer,differential scanning calorimetry,electrical conductivity test,and tensile test.The results show that Mg_(2)Si andβ-AlFeSi are the main intermetallic compounds in the as-cast structure,and Mg solute microsegregation is predominant inside the dendrite cell.The prediction of the full dissolution time of Mg_(2)Si by a kinetic model is consistent with the experiment.Theβ-AlFeSi in the alloy exhibits high thermal stability and mainly undergoes dissolution and coarsening during homogenization at 560℃,and only a small portion is converted toα-AlFeSi.The optimal homogenization parameters are determined as 560℃and 360 min,when considering the evolution of microstructure and resource savings.Both the strength and ductility of the alloy increased after homogenization.

Friction surfacing of hypereutectic Al-Si alloy on commercially pure aluminum : Effect of consumable rod heat treatment and heat input

This study investigated the effect of pre-friction surfacing heat treatment of consumable rods and heat input during friction surfacing on the microstructure,mechanical properties,and wear resistance of hypereutectic Al-Si alloy deposited on a commercially pure aluminum substrate.The results show that regardless of the consumable rod’s heat treatment conditions,the coating’s efficiency has increased with the increase in heat input,so the coating efficiency increases by 20%and 30%in the solid solution-treated rod and the artificially aged rod,respectively.By increasing the heat input,the average grain size in the coating fabricated by solid solution-treated rod and artificially aged rod increased from 0.1 to 0.9μm and from 0.2 to 1.3μm,respectively.At constant heat input,the average hardness and wear resistance of the coating created in the solid solution-treated rod are lower than those of the artificially aged rod.By decreasing heat input,the wear loss in the coating fabricated by solid solution-treated rod and artificially aged rod decreased by 10%and 20%,respectively,reaching 0.1 and 0.03μg/m.

Effect of Ni on microstructure and mechanical properties of Al−Mg−Si alloy for laser powder bed fusion

The microstructures and mechanical properties were systematically studied for the high-strength Al−5Mg_(2)Si−1.5Ni alloy fabricated by laser powder bed fusion(L-PBF).It is found that the introduction of Ni(1.5 wt.%)into an Al−5Mg_(2)Si alloy can significantly improve the L-PBF processibility and provide remarkable improvement in mechanical properties.The solidification range of just 85.5 K and the typical Al−Al3Ni eutectics could be obtained in the Ni-modified Al−5Mg_(2)Si samples with a high relative density of 99.8%at the volumetric energy density of 107.4 J/mm^(3).Additionally,the refined hierarchical microstructure was mainly characterized by heterogeneousα-Al matrix grains(14.6μm)that contain the interaction between dislocations and Al−Al3Ni eutectics as well as Mg_(2)Si particles.Through synergetic effects of grain refinement,dislocation strengthening and precipitation strengthening induced by Ni addition,the L-PBFed Al−5Mg_(2)Si−1.5Ni alloy achieved superior mechanical properties,which included the yield strength of(425±15)MPa,the ultimate tensile strength of(541±11)MPa and the elongation of(6.2±0.2)%.

Crack elimination and strength enhancement mechanisms of selective laser melted Si-modified Al−Mn−Mg−Er−Zr alloy

In order to increase the processability and process window of the selective laser melting(SLM)-fabricated Al−Mn−Mg−Er−Zr alloy,a novel Si-modified Al−Mn−Mg−Er−Zr alloy was designed.The effect of Si alloying on the surface quality,processability,microstructure,and mechanical properties of the SLM-fabricated alloy was studied.The results showed that introducing Si into the Al−Mn−Mg−Er−Zr alloy prevented balling and keyhole formation,refined the grain size,and reduced the solidification temperature,which eliminated cracks and increased the processability and process window of the alloy.The maximum relative density of the SLM-fabricated Si/Al−Mn−Mg−Er−Zr alloy reached 99.6%.The yield strength and ultimate tensile strength of the alloy were(371±7)MPa and(518±6)MPa,respectively.These values were higher than those of the SLM-fabricated Al−Mn−Mg−Er−Zr and other Sc-free Al−Mg-based alloys.

Morphology modification of Mg_2Si by Sr addition in Mg-4%Si alloy

A modification of Mg2Si in the hypereutectic Mg-4%Si alloy（mass fraction） with Sr was investigated.Two types of Mg2Si in the alloys were found：polygonal primary Mg2Si and Chinese script type eutectic Mg2Si.Adding Al-10% Sr master alloy to the Mg-4%Si alloy clearly reduced the average size of primary Mg2Si and changed the morphology of eutectic Mg2Si from Chinese script type to polyhedral or fine fibre shape.The refinement of primary Mg2Si is mainly attributed to the heterogeneous nucleation mechanism induced by the Sr-rich particles.The modification of eutectic Mg2Si results from the dissolved Sr,which alters the preferred growth manner of the eutectic.

Growth mechanism of primary silicon in cast hypoeutectic Al-Si alloys

The microstructural features of hypoeutectic AI-10%Si alloy were observed using optical microscopy and electron backscatter diffraction. The results show that primary silicon particles are frequently found in hypoeutectic alloys. Hence, the nucleation and growth mechanisms of the precipitation of primary silicon of hypoeutectic Al-10%Si alloy melts were investigated. It was discovered that Si atoms are easy to segregate and form Si-Si clusters, which results in the formation of primary silicon even in eutectic or hypoeutectic Al-Si alloys. In addition, solute redistribution caused by chemical driving force and large pile-ups or micro-segregation of the solute play an important role in the formation of the primary silicon, and the solute redistribution equations were derived from Jackson-Chalmers equations. Once Si solute concentration exceeds eutectic composition, primary silicon precipitates are formed at the front of solid/liquid interface.

Grain refining mechanism of Al-3B master alloy on hypoeutectic Al-Si alloys

Al-3B master alloy is a kind of efficient grain refiner for hypoeutectic Al-Si alloys. Experiments were carried out to evaluate the effect of undissolved AlB2 particles in Al-3B master alloy on the grain refinement of Al-7Si. It is found that the number and the settlement of AlB2 particles in the melt all have effect on the grain refining efficiency. On the basis of experiments and theoretical analysis, a new grain refinement mechanism was proposed to explain the grain refinement action of Al-3B on hypoeutectic Al-Si alloys. The formation of ＇Al-AlB2＇ shell structure is the direct reason for grain refinement and the undissolved AlB2 particles is the indirect nucleating base for subsequent α（Al） phase.

Effect of heat treatment on microstructure and tensile properties of A356 alloys

Two heat treatments of A356 alloys with combined addition of rare earth and strontium were conducted.T6 treatment is a long time treatment（solution at 535 ℃ for 4 h ＋ aging at 150 ℃ for 15 h）.The other treatment is a short time treatment（solution at 550 ℃ for 2 h ＋ aging at 170 ℃ for 2 h）.The effects of heat treatment on microstructure and tensile properties of the Al-7%Si-0.3%Mg alloys were investigated by optical microscopy,scanning electronic microscopy and tension test.It is found that a 2 h solution at 550 ℃ is sufficient to make homogenization and saturation of magnesium and silicon in α（Al） phase,spheroid of eutectic Si phase.Followed by solution,a 2 h artificial aging at 170 ℃ is almost enough to produce hardening precipitates.Those samples treated with T6 achieve the maximum tensile strength and fracture elongation.With short time treatment（ST）,samples can reach 90% of the maximum yield strength,95% of the maximum strength,and 80% of the maximum elongation.

Nucleation and growth of eutectic cell in hypoeutectic Al-Si alloy

The nucleation and growth of eutectic cell in hypoeutectic Al-Si alloy was investigated using optical microscopy and scanning electron microscopy equipped with electron backscattering diffraction（EBSD）.By revealing the eutectic cells and analyzing the crystallographic orientation,it was found that both the eutectic Si and Al phases in an eutectic cell were not single crystal,representing an eutectic cell consisting of small ＇grains＇.It is also suggested that the eutectic nucleation mode can not be determined based on the crystallographic orientation between eutectic Al phases and the neighboring primary dendrite Al phases.However,the evolution of primary dendrite Al phases affects remarkably the following nucleation and growth of eutectic cell.The coarse flake-fine fibrous transition of eutectic Si morphology involved in impurity elements modification may be independent of eutectic nucleation.

Corrosion mechanism associated with Mg_2Si and Si particles in Al-Mg-Si alloys

The electrochemical behaviors and coupling behaviors of the Mg2Si and Si phases with α（Al） were investigated, the corrosion morphologies of Al alloys containing Mg2Si and Si particles were observed, and the corrosion mechanism associated with them in Al-Mg-Si alloys was advanced. The results show that Si particle is always cathodic to the alloy base, Mg2Si is anodic to the alloy base and corrosion occurs on its surface at the beginning. However, during its corrosion process, the preferential dissolution of Mg and the enrichment of Si make Mg2Si transform to cathode from anode, leading to the anodic dissolution and corrosion of the alloy base at its adjacent periphery at a later stage. As the mole ratio of Mg to Si in an Al-Mg-Si alloy is less than 1.73, it contains Mg2Si and Si particles simultaneously in the grain boundary area, and corrosion initiates on the Mg2Si surface and the precipitate-free zone （PFZ） at the adjacent periphery of Si particle. As corrosion time is extended, Si particle leads to severe anodic dissolution and corrosion of the PFZ at its adjacent periphery, expedites the polarity transformation between Mg2Si and the PFZ and accelerates the corrosion of PFZ at the adjacent periphery of Mg2Si particle.

Microstructure evolution of spray-formed hypereutectic Al-Si alloys in semisolid reheating process

The Al-27%Si alloy was prepared by the spray forming process,and its microstructure evolution during the semisolid reheating process was investigated.The results show that,the primary Si phase coarsens during the reheating process and the coarsening rate increases with the increase of reheating temperature.The eutectic phase is produced in the molten region when quenched in the cold water.The microstructure evolution in the semisolid state can be divided into three stages.The remarkable characteristic of the first stage is only a solid-state phase transformation process.However,the region around the α（Al） matrix gradually melts in the second stage.The primary Si in the liquid phase coarsens obviously,and the eutectic phase is produced in the molten region when the specimens are quenched in cold water.In the last stage,the same thing as that in the second stage happens except that all the α（Al） matrixes are melted.

Effect of minor Zr and Sc on microstructures and mechanical properties of Al-Mg-Si-Cu-Cr-V alloys

The effects of minor contents of Zr and Sc on the microstructures and mechanical properties of Al-Mg-Si-Cu-Cr-V alloy were studied. The results show that the effects of minor Zr and Sc on the as-cast grain refinement in the ingots, the improvement in the strength of the as-extruded alloys and the restriction of high angle grain boundaries in the aged alloys can be sorted as Al3ScAl3 （Zr,Sc）Al3Zr. None of them could stop the nucleation of recrystallization, but Al3 （Zr,Sc） phase is a more effective inhibitor of dislocation movement compared to Al3 Sc in the aged alloys. Compared with the mechanical properties of the aged alloy added only 0.15% Sc, the joint addition of Zr and Sc to the alloy leads to a very slight decrease in strength with even no cost of ductility. Taking both the production cost and the little bad influence on mechanical properties into consideration, an optimal content of Zr and Sc in the Al-Mg-Si-Cu-Cr-V alloy to substitute 0.15% Sc is 0.13% Zr＋0.03% Sc.

Effects of isothermal process parameters on semisolid microstructure of Mg-8%Al-1%Si alloy

A Mg-8%Al-1%Si alloy with semisolid microstructure was fabricated by isothermal heat treatment process. The effects of isothermal process parameters such as holding temperature and holding time on the microstructure of Mg-8%Al-1%Si alloy were investigated. The results show that a non-dendritic microstructure could be obtained by isothermal heat treatment. With increasing holding temperature from 560 to 575 °C or holding time from 5 to 30 min, the liquid volume fraction increases, the average size of α-Mg grains grows larger and globular tendency becomes more obvious. In addition, the Mg2Si phase transforms from Chinese script shape to granule shape. The morphology modification mechanisium of Mg2Si phase in Mg-8%Al-1%Si alloy during the semisolid isothermal heat treatment was also studied.