Effect of hot extrusion on microstructures and mechanical properties of SiC nanoparticles reinforced magnesium matrix composite

Particulate reinforced magnesium matrix nanocomposite prepared with semisolid stirring assisted ultrasonic vibration was subjected to extrusion at 350 °C with an extrusion ratio of 12:1. Extrusion of the SiCp/AZ91 nanocomposite induced large scale dynamic recrystallization resulting in a fine matrix microstructure. There were two kinds of zones in the extruded nanocomposite: SiC nanoparticle bands parallel to the extrusion direction and refined-grain zones between the SiC nanoparticle bands. In the SiC nanoparticle bands, there were SiC nanoparticles along the boundaries of refined grains. The distribution of SiC nanoparticles was uniform although some agglomerates of SiC nanoparticles still existed in the SiC nanoparticle bands. The ultimate tensile strength, yield strength and elongation to fracture of the SiCp/AZ91 nanocomposite were simultaneously improved by extrusion. Results from the extruded SiCp/AZ91 nanocomposite tensile testing at different temperatures (75, 125, 175 and 225 °C) revealed an increase of the tensile strength and ductility values compared with the unreinforced and extruded AZ91 alloy.     

热挤压对不同搅拌时间制备的纳米SiCp/Mg-9Al-1Zn复合材料组织和性能的影响

通过半固态搅拌铸造和热挤压变形复合工艺制备出了质量分数为1%的纳米SiCp/Mg-9Al-1Zn镁基复合材料。研究了搅拌时间分别为10min和30min时对纳米SiCp/Mg-9Al-1Zn镁基复合材料的显微组织和力学性能的影响。结果表明,对于铸态的纳米SiCp/Mg-9Al-1Zn镁基复合材料来说,搅拌时间为30min时,基体的晶粒细化,但在晶界处析出的Mg17Al12相数量增多,网状化严重且SiC团聚增加,使得复合材料的力学性能下降。而通过热挤压后,复合材料形成了粗晶与细晶交替的组织结构。特别是对于搅拌时间为30min的复合材料,细晶区增多且纳米SiC颗粒分布更加均匀, 这就使得力学性能高于搅拌10min的挤压态的SiCp/Mg-9Al-1Zn复合材料。     

Fabrication of carbon nanotubes reinforced AZ91D composites by ultrasonic processing

Magnesium matrix nanocomposite reinforced with carbon nanotubes （CNTs/AZ91D） was fabricated by mechanical stirring and high intensity ultrasonic dispersion processing. The microstructures and mechanical properties of the nanocomposite were investigated. The results show that CNTs are well dispersed in the matrix and combined with the matrix very well. As compared with AZ91D magnesium alloy matrix, the tensile strength, yield strength and elongation of the 1.5%CNTs/AZ91D nanocomposite are improved by 22%, 21% and 42% respectively in permanent mold casting. The strength and ductility of the nanocomposite are improved simultaneously. The tensile fracture analysis shows that the damage mechanism of nanocomposite is still brittle fracture. But the CNTs can prevent the local crack propagation to some extent.     

Grain-Refined AZ92 Alloy with Superior Strength and Ductility

Grain-refined AZ92 (GR-AZ92) alloy with superior tensile properties is developed by adding 1 wt% Zn and a very small amount of SiC (0.17 wt%) to commercial AZ91 alloy for enhancing the solid-solution strengthening effect and refining the crystal grains, respectively. The homogenized GR-AZ92 alloy with an average grain size of 91 μm exhibits a tensile yield strength (TYS) of 125 MPa, ultimate tensile strength (UTS) of 281 MPa, and elongation of 12.1%, which are significantly higher than those of AZ91 alloy with a grain size of 420 μm (TYS of 94 MPa, UTS of 192 MPa, and elongation of 7.0%). The peak-aging time of GR-AZ92 alloy (8 h) is significantly shorter than that of AZ91 alloy (32 h) owing to a larger amount of grain boundaries in the former, which serve as nucleation sites of Mg₁₇Al₁₂ precipitates. A short-aging treatment for less than 1 h of the GR-AZ92 alloy causes an effective improvement in its strength without a significant reduction in its ductility. The 30-min-aged GR-AZ92 alloy has an excellent combination of strength and ductility, with a TYS of 142 MPa, UTS of 304 MPa, and elongation of 8.0%.     

The synergistic ability of Al2O3 nanoparticles to enhance mechanical response of hybrid alloy AZ31/AZ91

AZ31/AZ91 hybrid alloy nanocomposite containing Al₂O₃ nanoparticle reinforcement was fabricated using solidification processing followed by hot extrusion. The nanocomposite exhibited similar grain size to the monolithic hybrid alloy, reasonable Al₂O₃ nanoparticle distribution, non-dominant (0 0 0 2) texture in the longitudinal direction, and 25% higher hardness than the monolithic hybrid alloy. Compared to the monolithic hybrid alloy (in tension), the nanocomposite synergistically exhibited higher 0.2%TYS, UTS, failure strain and work of fracture (WOF) (+12%, +7%, +99% and +108%, respectively). Compared to the monolithic hybrid alloy (in compression), the nanocomposite exhibited higher 0.2%CYS and UCS, and lower failure strain and WOF (+5%, +3%, −7% and −7%, respectively). The beneficial effects of Al₂O₃ nanoparticle addition on the enhancement of tensile and compressive properties of AZ31/AZ91 hybrid alloy are investigated in this paper.     

SiC_p/AZ91镁基复合材料的热挤压

采用搅拌铸造法制备SiC体积分数为5%、10%和15%的颗粒增强AZ91镁基复合材料（SiCp/AZ91）。复合材料经过T4处理后,于350°C以固定挤压比12：1进行热挤压。在铸态复合材料中,颗粒在晶间微观区域发生偏聚。热挤压基本上消除了这种偏聚并有效地改善颗粒分布。另外,热挤压有效地细化基体的晶粒。结果表明：热挤压明显提高复合材料的力学性能。在挤压态复合材料中,随着SiC颗粒含量的升高,基体的晶粒尺寸减小,强度和弹性模量升高,但是伸长率降低。     

SiC颗粒增强AZ91基复合材料拉伸性能研究

针对风力发电机组摩擦材料对性能的要求,在不同的温度下,成功制备出了SiC颗粒增强的AZ91镁合金基复合材料,并且对其拉伸性能进行研究.结果表明,SiCp/AZ91复合材料的抗拉强度高于AZ91基体镁合金;在同样的烧结温度下,直径较小的SiC颗粒对复合材料的抗拉强度提高幅度较大.     

Investment casting of AZ91HP magnesium alloy

This paper describes AZ91HP magnesium alloy investment casting. The aim of this study is to optimize the process for magnesium investment casting. Special attention was given to evaluating the thermal stability of oxides against molten AZ91HP magnesium alloy. The oxides examined included CaO, CaZr0₃, and silica bonded A1₂0₃ and ZrSi0₄. Also, the microstructural features of the as-cast alloy were investigated, and the effect of the processing parameters on the microstructure and mechanical properties were evaluated describing the grain size, hardness and ultimate tensile strength of the as-cast alloy.     

Effects of Ce and Sb on the microstructure and properties of AZ91D magnesium alloy prepared by the EPC process

The effects of small amounts of cerium and antimony additions on the microstructure and the mechanical properties of AZ91D（Mg-9Al-Zn） based alloy were researched via the expendable pattern casting（EPC） process.The results show that the microstructure is obviously refined and the tensile strength of the AZ91D based alloy at ambient temperature is significantly improved.When compared to AZ91D,the AZ91D-1.0?-0.4%Sb alloy has higher ultimate tensile strength and elongation.Its ultimate tensile strength and elongation are enhanced by 39% and 47%,respectively.The morphology of the tensile fracture of the AZ91D-1.0?-0.4%Sb alloy has more characteristics of quasi-cleavage.This indicates that it has had a larger plastic deformation before failure.The tensile strength and elongation decrease with the increase of Ce and Sb contents because of the coarsening and volume increase of CeSb and Al11Ce3 phases.     

纳米SiC增强AZ91D复合材料高温拉伸及断裂行为

采用复合分散铸造法制备了纳米SiC颗粒(n-SiCp)增强AZ91D复合材料,研究了复合材料在高温下的拉伸及断裂行为。结果表明:n-SiCp的加入可以提高复合材料的高温拉伸强度,高温下n-SiCp对复合材料的增强效果比室温更加明显;n-SiCp的加入还显著提高了复合材料在高温下的断后伸长率,复合材料具有较好的高温塑性。断口分析表明,n-SiCp的加入使复合材料在高温下的断裂行为由室温的脆性断裂为主转化为典型的韧性断裂。     

基于纳米压痕法分析无铅焊点内Cu6Sn5金属化合物的力学性能

采用纳米压痕技术对微电子封装中无铅焊点内界面化合物(IMC) Cu6Sn5的弹性模量和硬度进行了测试.根据实际工业工艺流程和服役工况,制备接近真实服役状态下的微电子封装中无铅焊点界面化合物试样;采用扫描电镜(SEM)和能量色散X射线荧光光谱仪(EDX)确定IMC的形貌和化学成分;利用连续刚度测量(CSM)技术,采用不同的加载速率对无铅焊点(Sn3.0Ag0.5Cu、Sn0.7Cu和Sn3.5Ag)内的界面化合物Cu6Sn5进行测量,得到载荷、硬度和弹性模量-位移曲线.根据纳米压痕结果确定Cu6Sn5的蠕变应力指数.     

Effect of rolling and heat treatment on tensile behaviour of wrought Al-SiCp composites prepared by stir-casting

Al 6061- and Al 7108-SiCp composites (Al-PMMC) were prepared by stir-casting with SiCp size of 8 and 15 μm and volume fraction (Vf) of 0–20%. These composites were then subjected to successive hot rolling at 450 °C using a strain rate of 1 s⁻¹ while the intermediate period of heating between each two successive rolling steps was 1 min to 1 h. Tensile test was conducted on the as-rolled composite strips with 3.0, 1.1 and 0.4 mm thicknesses using 81, 94 and 98% reductions, subsequently, with a tensile rate of 10 MPa s⁻¹. Different tensile properties including ultimate tensile strength UTS, Young's modulus and elongation, were determined. The tensile behaviour was analysed in view of matrix alloy type and SiCp size and Vf. The effect of T6 treatment on the microstructure and tensile properties was also presented. Generally, successive hot rolling resulted in decreasing casting defects such as void and SiCp agglomeration present in the as-cast composites and hence enhanced mechanical properties were achieved. Almost 240 and 390% improvement in ultimate tensile strength (UTS) for 6061 and 7108 composite was obtained, respectively. The improvement in strength was remarkable for composites rolled to 0.4 mm. Annealing improved the elongation% at break of the 10–15% Vf composite more than 3 times. UTS of rolled composite was enhanced by T6 treatment at 176 °C and 120 °C for 6061 and 7108 composites. The effect of T6 treatment on the composite tensile behaviour was discussed.     

挤压铸造AZ81镁合金均匀化热处理工艺研究

为改善挤压铸造AZ81镁合金组织的不均匀性,对铸态试样进行均匀化热处理。采用金相显微镜、X射线衍射仪和扫描电镜对AZ81镁合金的组织与性能进行分析。结果表明:经400℃、8h均匀化处理后,AZ81合金有效地消除了枝晶偏析,改善了材料的组织状态;合金硬度由HRE73.72下降到HRE57.68,屈服强度由130MPa增加到138MPa,抗拉强度由226MPa增加到258MPa,伸长率则由7.6%增加到13.6%;试样的室温拉伸断口均为准解理断裂,经均匀化处理后断裂方式由沿晶界的脆性断裂转变为韧性穿晶断裂。     

Effect of heat treatment on microstructure and properties of semi-solid squeeze casting AZ91D

Semi-solid AZ91D magnesium alloy billets were prepared by near-liquidus heat holding. Semi-solid squeeze casting was conducted at 575, 585 and 595 ℃, respectively, with 1 mm·s~(-1) squeeze speed. The semisolid squeeze casting AZ91D samples were heat treated by T4(solution at 415 ℃ for 24 h) and T6(solution at 415 ℃ for 24 h + 220 ℃ for 8 h) processes, respectively. The microstructure and mechanical properties of the alloy in different states were investigated by means of OM, SEM and tensile testing machine. The results show that compared to as-cast alloy, the grain size of the semi-solid squeezed AZ91D decreased significantly, and with the increase of semi-solid squeeze temperature, the grain size of AZ91D increased. The grains of the alloy were refined by T4 treatment, and further refined by T6 treatment. T6 treatment greatly improved the tensile strength, elongation, and hardness, but did not significantly improve yield strength. After 575 ℃ squeeze casting and T6 treatment, the ultimate tensile strength(UTS) reached 285 MPa, the elongation reached 13.36%, and the hardness also reached the maximum(106.8 HV), but the yield strength(YS) was only 180 MPa. During the process of semi-solid squeeze casting and heat treatment, the matrix grain was refined and a large number of precipitated and secondary precipitated phases of Mg_(17)Al_(12) appeared. Both the average size of matrix grain and secondary precipitated phase decreased, while the volume fraction of secondary precipitated phase increased. All these resulted in high tensile strength, elongation and hardness.     

纳米SiC颗粒增强镁基复合材料的动态断裂行为研究

采用机械搅拌与高能超声处理相结合的分散法制备了纳米SiC颗粒增强AZ91D镁基复合材料(n-SiCp/AZ91D),利用动态SEM原位拉伸方法研究了纳米复合材料的断裂行为.结果表明:微裂纹主要在晶界上的β-Mg17Al12处萌生,并沿着晶界上的脆性相不断开裂和连接向前扩展,由于颗粒和界面的阻碍,裂纹扩展路径较长.AZ91D合金的裂纹也主要沿着晶界上的脆性相不断向前扩展,但裂纹扩展路径比较平坦,AZ91D合金在加载初期就萌生出大量的裂纹.     

Non-flux purification behavior of AZ91 magnesium alloy

The effects of non-flux purification techniques on the mechanical properties and microstructure of AZ91 magnesium alloy were investigated by ICP,OM,XRD and SEM.The results show that Ar spraying with high flow rate could remove non-metallic inclusions and improve the mechanical properties of AZ91.The alloy obtains the best properties after argon spraying for 30 min at the melt temperature of 740 °C.The ceramic foam filter(CFF) could effectively improve the ultimate tensile strength and elongation of AZ91 alloy,especially the elongation,which increase with increasing pores per inch(ppi) and the thickness of CFF.Non-flux purification does not change the microstructure of AZ91 alloy.However,filtration has a certain effect on the fracture pattern of AZ91 alloy.To improve the mechanical properties effectively,both filtration and gas spraying should be utilized together.     

添加Bi对AZ80镁合金显微组织及力学性能的影响(英文)

研究添加Bi对AZ80镁合金铸态显微组织及力学性能的影响。结果表明:将Bi加入到AZ80镁合金中后,粗大的β-Mg17Al12离异共晶组织被细化并由连续网状分布变为断续状;晶界处和枝晶间出现具有六方D52结构的针状和颗粒状的Mg3Bi2相。力学性能测试结果表明:随着Bi含量的增加,抗拉强度和伸长率先升高再降低,AZ80-0.5%Bi合金的综合力学性能最优;当Bi含量超过1.0%(质量分数)时,针状相明显变多并粗化,加载时容易开裂而割裂基体,导致力学性能降低。     

Effect of Micro- and Nano-SiC Particulate Reinforcements in Magnesium-Based Metal Matrix Composites

The effects of the volume ratios of micro and nano-SiC particles (SiCp) on the grain refinement, distribution of SiCp particle, and tensile properties of the as-cast AZ31B (Mg-3Al-1Zn-0.3Mn) magnesium-based metal matrix composites have been investigated. As the volume fraction of micron SiCp decreases to 9 vol.% and the nano-SiCp increases to 1 vol.%, excellent grain refinement effect is achieved. This is due to both the uniform distribution and refining effects of micro- and nano-SiCp. Moreover, the micron SiCp distribute along the grain boundaries, while nano-SiCp is mainly distributed around the micron SiCp. The room-temperature tensile results show that the optimal room-temperature yield and tensile strengths are achieved with a 9/1 ratio of micro to nano-SiCp, while the 9.5/0.5 ratio yielded the highest elongation.     

Effect of Hot Extrusion on Microstructures and Properties of TiB2/AZ31 Magnesium Based Composites

采用原位合成-半固态搅拌铸造法制备了TiB2/AZ31镁基复合材料,研究了热挤压对TiB2/AZ31镁基复合材料组织和力学性能的影响。结果表明：热挤压不仅能显著细化合金组织,而且能有效改善TiB2颗粒分布的均匀性。与铸态AZ31镁合金相比,铸态TiB2/AZ31镁基复合材料的硬度、抗拉强度都有一定程度的提高。经过热挤压后,TiB2/AZ31镁基复合材料的硬度和抗拉强度分别比基体合金提高了126.2%和98.8%,达到950 MPa和322 MPa。磨损表面形貌显示,TiB2颗粒的引入以及对TiB2/AZ31镁基复合材料进行热挤压,都可有效地提高材料的耐磨性。     

Microstructure and Mechanical Properties of CNT-Reinforced AZ91D Composites Fabricated by Ultrasonic Processing

Carbon nanotube(CNT)-reinforced AZ91 D alloy composite was fabricated by ultrasonic processing.The microstructure and mechanical properties of the CNTs/AZ91 D composites were investigated.Obvious grain refinement was achieved with the addition of 0.5 wt%CNTs.The SEM observation indicated that CNTs were distributed near the grain boundary or around the inter-grain β-Mg_(17)Al_(12) phase.No evident reaction product was found at the interface between CNTs and AZ91 D matrix.Compared to the monolithic AZ91 D alloy,the yield strength,ultimate tensile strength,and elongation of the 0.5 wt%CNTs/AZ91 D composite were improved significantly.However,the poor interface bonding between CNTs and AZ91 D matrix restricted further improvement in mechanical properties.