The effect of Sr and Fe additions on the microstructure and mechanical properties of a direct squeeze cast Al-7Si-0.3Mg alloy

This article describes the results of an investigation into the microstructure and mechanical properties of a gravity die cast and direct squeeze cast LM25 alloy (Al-7Si-0.3Mg-0.3Fe). The direct squeeze cast LM25 alloy has superior mechanical properties compared to the gravity die cast LM25 alloy, especially with regard to ductility, which is increased from ∼1.7 pct for the gravity die cast LM25 alloy to ∼8.0 pct for the direct squeeze cast LM25 alloy in the T6 heat-treated condition. This increase in ductility is due to (1) the removal of porosity, (2) a decrease in Si particle size, and (3) a refinement of the Fe-Si-aluminide particles. High cooling rates in direct squeeze casting result in quench modification of the Si particles, such that chemical modification with Sr or Na may not be required. In addition, direct squeeze casting is more tolerant of Fe impurities in the alloy, due to the formation of smaller Fe-Si-aluminide particles than those in gravity die cast material. The direct squeeze cast LM25+Fe alloy (Al-7Si-0.3Mg-1.0Fe) has a ductility of ∼6.5 pct, compared to that of ∼0.5 pct for the gravity die cast LM25 + Fe alloy in the T6 heat-treated condition. This increase in tolerance to Fe impurities can lead to a substantial reduction in manufacturing costs due to (1) reduced raw-material costs, (2) reduced die sticking, and (3) improved die life.     

Modeling of feeding behavior of solidifying Al-7Si-0.3Mg alloy plate casting

The systematic change of riser size, together with the variation of geometries of solidifying Al-7Si-0.3Mg plate castings, was tested by thermal analysis to model the interdendritic feeding behavior based on Darcy’s law. This law, however, is found to be only applicable to certain thermal conditions in the solidifying casting. The applicability of Darcy’s law depends on the regime of solidification time. A new feeding efficiency parameter integrating all individual ther-mal variables, denoted as(G · t ^2/3)V_s (whereG is the thermal gradient,t is local solidification time, and V_{s i} is solidus velocity), is found satisfactory to predict the formation of porosity. The combined geometries of a casting and its riser size exert a great influence on the thermal vari-ables of Al-7Si-0.3Mg alloy in a complicated way. Together, these thermal variables synergize to govern the feeding behavior of the casting.     

球磨时间对纳米晶Al-7Si-0.3Mg合金粉末微观组织及硬度的影响

以机械破碎Al-7Si-0.3Mg合金粉末为原料进行高能球磨, 对不同球磨时间的合金粉末进行金相观察、X射线衍射分析、透射电镜表征及显微硬度测试, 研究球磨时间对纳米晶Al-7Si-0.3Mg合金粉末的影响。结果发现, 高能球磨导致共晶硅颗粒从微米尺度细化到亚微米尺度, 颗粒形状从多面体转变成圆形, 颗粒内部有层错生成。随着球磨时间逐渐增加到60 h, 合金粉末平均颗粒尺寸从134μm逐渐下降到22μm, Al(Si, Mg)基体晶粒尺寸从438 nm降低到23 nm, 粉末显微硬度从HV 93增加到HV 289。粉末硬度的增加主要归功于球磨导致的晶粒细化(细晶强化作用), 此外, 球磨过程中硅颗粒的细化以及球磨引起的Mg、Si原子在基体内固溶度的增加也有利于粉末硬度的提高。     

微量元素对Al-1.2Mg-1.3Si-0.6Cu-0.3Mn铝合金组织性能的影响

The effects of impurity element of Fe and microelements of Zn, Cr and Ti on the constituents,dispersoids, grain size, mechanical properties and formability of Al-1.3Mg-1.2Si-0. 6Cu-0. 3Mn alloy were investigated in the present work by analyzing microstructures, phase composition, mechanical tests. The resuits indicated that with the increase of Fe content, the insoluble constituents increased, and the mechanical properties and r15 of alloy sheets debased, which can be recovered by the addition of microelements Zn, Cr and Ti. Al-1.3Mg-1.2Si-0. 6Cu-0. 3Mn alloy sheets in the T4 temper are difficult to strengthen with paint -bake treatment in automobile factory.     

Optimization of Solution Treatment of Cast Al-7Si-0.3Mg and Al-8Si-3Cu-0.5Mg Alloys

The influence of solidification rate on the solution-treatment response has been investigated for an Al-7Si-0.3Mg alloy and an Al-8Si-3Cu-0.5Mg alloy. The concentrations of Mg, Cu, and Si in the matrix after different solution-treatment times were measured using a wavelength dispersive spectrometer. All Mg dissolves into the matrix for the Al-Si-Mg alloy when solution treated at 803 K (530 °C) because the π-Fe phase is unstable and transforms into short β-Fe plates which release Mg. The Q-Al₅Mg₈Cu₂Si₆ phase do not dissolve completely at 768 K (495 °C) in the Al-Si-Cu-Mg alloy and the concentration in the matrix reached 0.22 to 0.25 wt pct Mg. The distance between π-Fe phases and Al₂Cu phases was found to determine the solution-treatment time needed for dissolution and homogenization for the Al-Si-Mg alloy and Al-Si-Cu-Mg alloy, respectively. From the distance between the phases, a dimensionless diffusion time was calculated which can be used to estimate the solution-treatment times needed for different coarsenesses of the microstructure. A model was developed to describe the dissolution and homogenization processes.     

Influence of Grain Refinement on Slurry Formation and Surface Segregation in Semi-solid Al-7Si-0.3Mg Castings

This study aims to evaluate the effect of grain refinement on slurry formation and surface segregation in semi-solid castings produced by the Rheometal™ process. The effect of two grain refiners, Al-8B and Al-5Ti-1B, on the slurry α-Al grain size, shape factor and solid fraction was evaluated. The results suggest that the addition of a grain refiner can affect the solid fraction obtained in the Rheometal^TM process and, consequently, reduce the solute content near the casting surface. Grain refiner addition resulted in a larger fraction of α-Al grains ≤ 60 µm for the refined alloys compared with the unrefined alloy. Additionally, the growth of α-Al slurry globules was greater for the unrefined alloy compared with the refined alloy during solidification in the die-cavity. A more homogeneous and finer microstructure was observed near the surface in the grain-refined castings compared with the unrefined castings. Evidence of significant liquid penetration was identified in some α-Al globules, indicating that disintegration of α-Al globules may occur during the Rheometal™ casting process.

     

Eutectic Morphology of Al-7Si-0.3Mg Alloys with Scandium Additions

The mechanisms of Al-Si eutectic refinement due to scandium (Sc) additions have been studied in an Al-7Si-0.3Mg foundry alloy. The evolution of eutectic microstructure is studied by thermal analysis and interrupted solidification, and the distribution of Sc is studied by synchrotron micro-XRF mapping. Sc is shown to cause significant refinement of the eutectic silicon. The results show that Sc additions strongly suppress the nucleation of eutectic silicon due to the formation of ScP instead of AlP. Sc additions change the macroscopic eutectic growth mode to the propagation of a defined eutectic front from the mold walls opposite to the heat flux direction similar to past work with Na, Ca, and Y additions. It is found that Sc segregates to the eutectic aluminum and AlSi₂Sc₂ phases and not to eutectic silicon, suggesting that impurity-induced twinning does not operate. The results suggest that Sc refinement is mostly caused by the significantly reduced silicon nucleation frequency and the resulting increase in mean interface growth rate.     

轧制变形量对Ti-45Al-7Nb-0.3W合金组织与性能的影响

利用X衍射分析(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、室温拉伸试验等手段,研究粉末冶金Ti-45Al-7Nb-0.3W(原子分数,%)合金包套轧制过程中的显微组织和力学性能的变化规律。结果表明:热等静压法态的Ti-45Al-7Nb-0.3W合金组织为近γ组织,主要由块状的γ相组成,同时包括少量的α2相及极少量的B2相。轧制后Ti Al合金板材为双态组织,B2相消失。随轧制变形量增加,合金板材强度增加,变形量为40%时,板材抗拉强度最大,达到955 MPa。继续增加变形量合金板材的力学性能有所降低。当变形量较小时,合金的塑性变形主要通过位错滑移和攀移来实现。随变形量增加,孪生和动态再结晶机制发挥作用。     

固溶处理对Al-1.5Si-1.2Mg-0.6Cu-0.3Mn铝合金组织性能的影响

对汽车车身板用Al-1.5Si-1.2Mg-0.6Cu-0.3Mn铝合金冷轧薄板进行了固溶处理,研究了固溶温度、时间对第二相、晶粒及成形性能的影响规律.结果表明:在500～555℃之间进行固溶处理时,固溶温度升高,基体中残留的第二相数量逐渐减少,而再结晶晶粒尺寸形态变化不大;合金板材的强度和延伸率单调增大,,IE单调减小,n,r15变化不大.1.2 mm厚的冷轧合金薄板在540℃固溶处理时,保温时间需接近30 min才可使其具有良好的成形性,继续延长保温时间至180 min其成形性能变化不大.1.2 mm厚的A1-1.5Si-1.2Mg-0.6Cu-0.3Mn铝合金冷轧薄板合适的固溶处理温度为540℃,保温时间应接近30 min.常规T4状态的6xxx系铝合金薄板直接在汽车厂冲压成形后的烤漆涂装处理并不能起到提高车身构件强度的作用.     

喷射沉积Al-12Si-0.6Mg合金的微观组织与性能

共晶合金具有良好的激光焊接性能,为提高电子封装盖板用Al-12Si合金的强度并保持良好的热物理性能,采用喷射沉积与热压烧结技术制备Al-12Si合金,研究添加0.6％Mg对合金微观组织、力学性能和热物理性能的影响.结果表明,喷射沉积/热压烧结Al-12Si合金中Si相呈近球形颗粒,平均直径为(4.5±0.2)μm,均匀...     

Microstructure and mechanical properties of Al-7Si-0.7Mg alloy formed with an addition of(Pr+Ce)

Effects of(Pr+Ce) addition on the Al-7Si-0.7Mg alloy were investigated by optical microscope(OM), energy diffraction spectrum(EDS), X-ray diffraction(XRD) and tensile tests. The results showed that the Al-7Si-0.7Mg alloy was modified with(Pr+Ce) addition. The needle-like eutectic silicon phase developed into rose form and the crystalline grains decreased in size and showed a high degree of spheroidization. When the amount of the(Pr+Ce) addition reached 0.6 wt.%, the mean diameter was 31.8 μm(refined by 50%). The aspect ratio decreased to 1.35, and the tensile strength and ductility reached 192.4 MPa and 2.18%, respectively. At higher levels of addition, over-modification occurred, as indicated by increased grain size and reduced mechanical properties. The poisoning effect of the(Pr+Ce) addition on eutectic silicon and the constitutional supercooling caused by the(Pr+Ce) addition were the major causes of alloy modification, grain refinement, and the improvement of mechanical properties.     

The effect of mischmetal addition on the structure and mechanical properties of a cast Al-7Si-0.3Mg alloy containing excess iron (up to 0.6 Pct)

The effect of Fe content (0.2 to 0.6 pct) on the microstructure and mechanical properties of a cast Al-7Si-0.3Mg (LM 25/356) alloy has been investigated. Further, 1 pct mischmetal (MM) additions (a mixture of rare-earth (RE) elements) were made to these alloys, and their mechanical properties at room and at elevated temperatures (up to 200 °C) were evaluated. A structure-property correlation on this alloy was attempted using optical microstructure analysis, fractographs, X-ray diffraction, energy-dispersive analysis of X-rays (EDX), and quantitative metallography by image analysis. An increase in Fe content increased the volume percentage of Fe-bearing intermetallic compounds (β and π phases), contributing to the loweryield strength (YS), ultimate tensile strength (UTS), percentage elongation, and higher hardness. An addition of 1 pct MM to the alloys containing 0.2 and 0.6 pct Fe was found to refine the microstructure; modify the eutectic silicon and La, Ce, and Nd present in the MM; form different intermetallic compounds with Al, Si, Fe, and Mg; and improve the mechanical properties of the alloys both at room and elevated temperatures.     

Effect of alloying elements on the solidification characteristics and microstructure of Al- Si- Cu- Mg- Fe 380 alloy

The effect of varying the major alloying elements within the limits of specification on the solidification behavior, fluidity, and microstructure of a 380 alloy has been studied at two cooling rates. The thermal analysis technique has been used to study the solidification behavior. The alloying elements investigated ranged from 3.22 to 4.09 pct copper, 1.01 to 1.70 pct iron, 0.06 to 0.50 pct magnesium, 1.69 to 3.00 pct zinc, and 0.16 to 0.46 pct manganese. The results show that the solidification behavior of the 380 alloys is complicated, and the cooling curve at 0.4 ‡C/s indicates six reactions taking place during the process of solidification. Cooling curves obtained for each of the alloying element additions, their analysis, and the resultant microstructures are discussed.     

形变热处理对Cu-6.5Ni-1Al-1Si-0.15Mg-0.15Ce合金微观组织及性能的影响

设计并制备 Cu-6.5Ni-1Al-1Si-0.15Mg-0.15Ce(wt.%)合金。采用光学显微镜(OM)、扫描电镜(SEM)、能谱分析和透射电镜(TEM)等测试手段研究合金形变热处理过程中微观组织及性能的变化。合金铸态组织为典型的枝晶组织,铸锭经过920℃热轧后,枝晶组织显著消除。合金的适宜固溶处理制度为960℃/4 h。该合金固溶处理后的冷变形对合金最终性能有很大影响。冷变形程度越大,合金达到硬度峰值的时间越短,硬度峰值和电导率越高。时效温度越高,时效析出过程越快。960℃固溶4 h后冷轧50%,450℃时效2 h硬度峰值可达300.8 HV,电导率20.6%IACS,抗拉强度963.9 MPa,屈服强度950.1 MPa。合金在时效过程中析出纳米级粒子为δ-Ni2Si,其与基体的位相关系为：Cuδ[001][001], Cuδ(110)(010), Cuδ(110)(100)。     

Effects of rolling deformation on microstructure and hardness of Ti-45Al-9Nb-0.3Y alloy

The microstructure evolution of as-rolled Ti-45Al-9Nb-0.3Y alloy as well as the nanohardness of β/B2 matrix was investigated by means of scanning electron microscopy(SEM) in backscattered electron mode(BSE) mode, transmission electron microscopy(TEM) and nanoindentation. This high Nb containing Ti Al based alloy was rolled with 50%, 60%, 65% reduction, respectively. Omega phase precipitated in B2 phase with an orientation relationship of {110}_β//{11 2 0}_ω and 11 1_β//0001_ω. Moreover, with the increase of deformation reduction, rod-like structure which was formed in γ grain transformed from(α_2+γ) lamellae structure into α_2 phase only. Additionally, nanoinentation experiment revealed that the precipitation hardening of ω phase increased the hardness of β/B2 phase.     

Effect of phosphorus modification on the microstructure and mechanical properties of DC cast Al-17.5Si-4.5Cu-1Zn-0.7Mg-0.5Ni alloy

Direct chill (DC) casting of an Al-17.5Si-4.5Cu-1Zn-0.7Mg-0.5Ni alloy with minor additions of Zr, V and Ti was performed and the effect of phosphorus modification on the solidification microstructure and mechanical properties were investigated. The results show that the addition of phosphorus refines the primary Si crystals remarkably but coarsens the eutectic Si in the DC cast billets. In the samples taken in 1/2 radius region of the billets of 100 mm in diameter, the average size of the primary Si particles in the unmodified alloy is 38 μm, while that in the modified alloys range from 13 to 26 μm, depending on the melt treatment time. The AlP particles as heterogeneous nucleation sites for the primary Si crystals were observed in the center of the primary Si particles. In the modified alloy, the achieved ultimate tensile strength is 320MPa and 433MPa respectively in the as-cast state and T6 state. The size of the primary Si particles is critical for the improvement of the mechanical properties of the alloy.     

Influence of casting technique and hot isostatic pressing on the fatigue of an Al-7Si-Mg alloy

The influence of the casting filling technique and hot isostatic pressing (hipping) on the fatigue-life distribution of Al-7Si-Mg alloy castings has been studied. To vary the number density and size of oxide-film defects in the castings, test bars were cast using bottom-gated filling systems with and without filtration. Some unfiltered castings were subjected to a hipping treatment of 100 MPa at 500 °C for 6 hours. Test pieces were machined from the castings and were fatigue tested in pull-pull sinusoidal loading, at maximum stresses of 150 and 240 MPa under a stress ratio of R=+0.1. The fatigue lives at any probability of failure and Weibull statistical parameters of the filtered castings were higher than those of the unfiltered and nonhipped castings, illustrating the importance of the casting technique. However, the unfiltered but hipped castings exhibited higher performance. It is proposed that the significant improvement in fatigue life after hipping is due to the deactivation of entrained double oxide-film defects as fatigue-crack initiators.     

石墨烯含量对石墨烯/Al-15Si-4Cu-Mg复合材料微观组织和力学性能的影响

低温球磨分散结合真空热压烧结工艺制备了石墨烯增强的Al-15Si-4Cu-Mg基复合材料.采用扫描电镜、X射线衍射、能谱分析和透射电镜表征了复合材料微观结构,通过抗拉强度和硬度测试,研究了石墨烯添加量对石墨烯/Al-15Si-4CuMg复合材料微观组织和力学性能的影响.结果表明:当石墨烯质量分数分别为0. 4%和0. 8%,石墨烯沿基体晶界均匀分布,钉扎晶界,石墨烯与Al-15Si-4Cu-Mg基体界面结合良好,初晶β-Si、Mg_2Si和Al_2Cu相弥散分布于基体中.当石墨烯质量分数上升至1%,石墨烯分散困难,过量石墨烯富集于晶粒边界处,诱发脆性鱼骨状Al_4Cu_2Mg_8Si_7相沿晶界析出.当石墨烯质量分数为0. 8%时,石墨烯/Al-15Si-4Cu-Mg复合材料的拉伸强度和硬度分别达到321 MPa和HV 98,相比纯Al-15Si-4Cu-Mg复合材料分别提高了19. 3%和46. 2%;当石墨烯质量分数为0. 4%时,复合材料的屈服强度高达221 MPa,硬度和塑性亦获得明显改善.     

石墨烯含量对石墨烯/Al-15Si-4Cu-Mg复合材料微观组织和力学性能的影响

低温球磨分散结合真空热压烧结工艺制备了石墨烯增强的Al-15Si-4Cu-Mg基复合材料.采用扫描电镜、X射线衍射、能谱分析和透射电镜表征了复合材料微观结构,通过抗拉强度和硬度测试,研究了石墨烯添加量对石墨烯/Al-15Si-4Cu-Mg复合材料微观组织和力学性能的影响.结果表明:当石墨烯质量分数分别为0.4%和0.8%,石墨烯沿基体晶界均匀分布,钉扎晶界,石墨烯与Al-15Si-4Cu-Mg基体界面结合良好,初晶β-Si、Mg₂Si和Al₂Cu相弥散分布于基体中.当石墨烯质量分数上升至1%,石墨烯分散困难,过量石墨烯富集于晶粒边界处,诱发脆性鱼骨状Al₄Cu₂Mg₈Si₇相沿晶界析出.当石墨烯质量分数为0.8%时,石墨烯/Al-15Si-4Cu-Mg复合材料的拉伸强度和硬度分别达到321 MPa和HV 98,相比纯Al-15Si-4Cu-Mg复合材料分别提高了19.3%和46.2%;当石墨烯质量分数为0.4%时,复合材料的屈服强度高达221 MPa,硬度和塑性亦获得明显改善.      

Microstructure and mechanical properties of spray-deposited Al-17Si-4.5Cu-0.6Mg wrought alloy

High Si content in Al-Si alloys usually leads to the formation of coarse, brittle Si phase under slow solidification conditions. In the present study, an Al-17Si-4.5Cu-0.6Mg (referred to hereafter as AS17) was synthesized using spray deposition to modify the Si phase. In the spray deposition process, the master alloy of AS17 was atomized using N₂ gas, and was deposited on a collecting substrate directly into a three-dimensional material. The microstructure and mechanical behavior of the spray-deposited AS17 were studied using optical microscopy (OM) scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction, and tensile tests. The present results indicate that in the spray-deposited AS17, the eutectic Si phase was modified from a “flakelike” morphology, characteristic of ingot metallurgy (IM) materials, into a “particulate” morphology. The formation of the coarse primary Si blocks was suppressed. Moreover, the size and morphology of Si particulates were found to have significant influences on the deformation behavior. During plastic deformation, extensive fracture of Si occurred. The percentage of fractured Si increased with the increasing amount of plastic deformation and the size of Si particulates. Finally, the room-temperature mechanical properties of the spray-deposited AS17 were compared with its IM counterpart A390 (an IM alloy with identical composition as AS17). The strength and ductility of AS17 were improved over those of A390. In the T6 condition, the yield strength and tensile elongation of AS17 were 503 MPa and 3.0 pct, respectively, whereas those of A390 were 374 MPa and 1.3 pet, respectively.