Microstructure and mechanical properties of AZ91D magnesium alloy by expendable pattern shell casting with different mechanical vibration amplitudes and pouring temperatures

To refine the microstructure and improve the mechanical properties of AZ91 D alloy by expendable pattern shell casting(EPSC),the mechanical vibration method was applied in the solidification process of the alloy.The effects of amplitude and pouring temperature on microstructure and mechanical properties of AZ91 D magnesium alloy were studied.The results indicated that the mechanical vibration remarkably improved the sizes,morphologies and distributions of the primaryα-Mg phase andβ-Mg17 Al12 phase,and the densification and tensile properties of the AZ91 D alloy.With an increase in amplitude,the microstructures were gradually refined,resulting in a continuous increase in mechanical properties of the AZ91 D alloy.While,with the increase of pouring temperature,the microstructures were continuously coarsened,leading to an obvious decrease of the mechanical properties.The tensile strength and yield strength of the AZ91 D alloy with a vibration amplitude of 1.0 mm and a pouring temperature of 730℃were 60%and 38%higher than those of the alloy without vibration,respectively.     

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.     

混合稀土对压铸AZ91D合金的组织及力学性能的影响

研究了不同添加量的混合稀土对压铸AZ91D合金的组织和力学性能的影响。添加混合稀土后,常温力学性能没有明显改善。在100℃时,混合稀土含量为0.4%的压铸AZ91D合金的力学性能与不含混合稀土的试样几乎相等。在170℃时,混合稀土含量为0.4%的压铸AZ91D合金的抗拉强度、屈服强度及伸长率分别为206MPa、142MPa、26%,比不含混合稀土的压铸AZ91D试样的力学性能分别提高15.7%、10%及30%。这是因为添加适量的混合稀土后,形成热稳定性较高的强化相,增加了位错滑移阻力并阻碍裂纹扩展,镁基体中稀土元素起到固溶强化作用,从而提高镁合金的高温抗拉强度。     

Magnesium matrix nanocomposites fabricated by ultrasonic assisted casting

Abstract

Magnesium matrix composites reinforced with nano-sized SiC particles (n-SiC_p/AZ91D) were fabricated by high intensity ultrasonic assisted casting. The microstructure of the nanocomposites was investigated by optical microscopy, scanning electronic microscopy (SEM), high resolution transmission electronic microscopy (HRTEM) and Energy Dispersive Spectroscopy (EDS) methods. The results showed that the dispersion and distribution of n-SiC_p in magnesium alloy melts were significantly improved by ultrasonic processing. Compared to the unreinforced AZ91D matrix, mechanical properties of the nanocomposites including tensile and yield strengths were remarkably improved and the yield strength increased by 117% after gravity permanent mould casting.     

Mechanical properties of thixomolded AZ91D magnesium alloy

Tensile properties of thixomolded AZ91D alloy were studied to investigate the fracture mechanism by the microstructure and decohesion surfaces of tensile specimens which were manufactured at different processing conditions including barrel temperature, shot velocity, mold temperature and screw rotation speed. The results revealed that mechanical properties of thixomolded AZ91D mainly depended on porosity level, the size and volume fraction of primary solid phase and the size of α-Mg and β-Mg₁₇Al₁₂ in liquid phase. The increase in barrel temperature and shot velocity would cause the increase of both strength and ductility, while increasing mold temperature or improving screw rotation speed was coupled by the reduction of tensile properties. The tensile behaviors for different processing parameters were reasonably interpreted through the dependant factors during the deformation.     

Microstructure and Mechanical Properties of AZ91 Alloys by Addition of Yttrium

Effects of yttrium (Y) on the microstructure and properties of as-cast Mg-Al-Zn (AZ91) alloys were studied. Y additions not only change the microstructure but also influence the mechanical properties of AZ91 alloy. AZ91 unmodified alloys under as-cast state indicate that eutectic phase Mg₁₇Al₁₂ is continuous and reticulated. Yttrium addition to AZ91 casting alloys has an important influence on the primary-phase and precipitation. When the Y content is 0.3 wt.%, no Y-containing compound was observed. When the Y content is 0.6 and 0.9 wt.%, Al₂Y phase formed in the alloy and the growth morphology of eutectic Mg₁₇Al₁₂ phase is modified. When the Y content is further increased to 1.2 wt.%, the Al₂Y phase becomes coarser and Mg₁₇Al₁₂ transforms into a cotton-shape structure. The results showed that Y can improve significantly as-cast microstructure of AZ91 alloys, refining Mg₁₇Al₁₂ phase and increasing in hardness and strength and decreasing in impact toughness and elongation.     

Fabrication of carbon nanotube reinforced AZ91D composite with superior mechanical properties

AZ91D alloy composites with 1.0% CNTs have been fabricated by a method combined ball milling with stirring casting. The composite was investigated using optical microscopy(OM), X-ray diffraction(XRD), Fourier transform infrared spectroscope (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM) and room temperature (RT) tensile test. The results show that CNTs were homogeneously distributed in the matrix and maintained integrated structure. The yield strength and ductility of AZ91D/CNTs composite were improved by 47.2% and 112.2%, respectively, when compared with the AZ91 alloy. The uniform distribution of CNTs and the strong interfacial bonds between CNT and the matrix are dominated to the simultaneous improvement of yield strength and ductility of the composite. In addition, the grain refinement as well as the finer β phase (Mg₁₇Al₁₂) with homogenous distribution in the matrix can also slightly assist to the enhancement of the mechanical properties of the composite.     

Microstructure and Elevated Temperature Properties of Die-cast AZ91-<Emphasis Type="Italic">x</Emphasis>Nd Magnesium Alloys

The effect of Nd addition on the microstructure and mechanical properties of a die-cast AZ91 alloy was investigated in the present work. The results show that the die-cast AZ91 alloy is composed of α-Mg matrix and γ-Mg₁₇Al₁₂ phase. Nd addition into the AZ91 alloy leads to the formation of rare earth containing intermetallic phase. Al₄Nd phase forms when Nd content is less than or equal to 1.0 wt.%. Al₂Nd phase appears simultaneously when Nd content reaches to 3.0 wt.%. The size and volume fraction of γ-Mg₁₇Al₁₂ phase decrease, because of the newly formed Al-Nd phase. And the γ-Mg₁₇Al₁₂ phase distributes from reticular to dispersive. Nd addition has a little effect on the room temperature properties of the die-cast AZ91 alloy, but greatly improves the elevated temperature properties. The tensile strength of AZ91-0.5Nd and AZ91-1.0Nd alloy tested at 150 °C is even close to the room temperature strength. The AZ91-1.0Nd alloy has the optimal properties.     

Microstructure evolution and mechanical properties of Mg-12Zn-2Y alloy containing quasicrystal phase fabricated by different casting processes

Although icosahedral quasicrystal phase (denoted as I-phase) has been verified as an outstanding reinforcing phase, the mechanical properties of quasicrystal-reinforced Mg-Zn-Y alloys fabricated by traditional casting processes are still unsatisfactory due to the serious segregation of intermetallic compounds. In this study, the microstructure and mechanical properties of Mg-12Zn-2Y alloy fabricated by different casting processes, including permanent mold casting, squeeze casting and rheo-squeeze casting with ultrasonic vibration, were systematically investigated and compared. The results show that massive, large-sized I-phase and Mg₇Zn₃ phase gather together in the permanent mold cast sample, while the squeeze casting process leads to the transformation of I-phase into fine lamellar morphology and the amount of Mg₇Zn₃ decreases. As to the rheo-squeeze casting process, when the ultrasonic vibration is exerted with power from 800 W to 1,600 W, the α-Mg grains are refined and spheroidized to a large extent, and the lamellar spacing of the eutectic structure is significantly reduced, accompanied by some tiny granular I-phase scattering in the α-Mg matrix. However, when the ultrasonic power continuously increases to 2,400 W, the eutectic structure becomes coarse. The best mechanical properties of the rheo-squeeze cast alloy are obtained when the ultrasonic power is 1,600 W. The microhardness, yield strength, ultimate tensile strength and elongation are 79.9 HV, 140 MPa, 236 MPa, and 3.25%, which are 44.1%, 26.1%, 25.5%, 132.1% respectively higher than the corresponding values of the squeeze casting sample, and are 47.6%, 44.3%, 69.8%, and 253.3% respectively higher than the corresponding values of the permanent mold casting sample.

     

Ca含量和流变挤压铸造工艺参数对AZ91-1Ce-xCa合金显微组织和力学性能的影响

首先,研究不同Ca含量AZ91-1Ce合金的显微组织、力学性能和阻燃性能,优化出最佳Ca含量.然后,系统研究流变挤压铸造工艺参数(包括压力和转速)对AZ91-1Ce-2Ca合金显微组织和力学性能的影响.结果表明,随着Ca含量的增加,AZ91-1Ce-xCa合金的显微组织细化,阻燃性能提高.但当Ca含量超过1％(质量分数...     

镁合金减震塔的真空压铸研究

研究并对比了真空压铸生产的AZ91D和AM60合金减震塔铸件的微观组织、力学性能,考察了热处理工艺对其性能的影响。结果表明,AZ91D和AM60真空压铸件组织均由基体α-Mg和Mg17Al12相组成,固溶处理后Mg17Al12相消失,时效处理后其以非连续相形式析出。AZ91D和AM60铸件均能够热处理强化,但是AM60合金的强化效果弱于AZ91D合金。另外,真空压铸能有效消除铸件中的气孔,但无法完全消除缩松现象,不过仍可通过热处理提高真空压铸件的力学性能。     

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.     

Nd对压铸AZ91D合金组织与性能的影响

传统压铸获得AZ91D和AZ91D-1.11Nd两种合金试样,采用光学金相显微镜、扫描电子显微镜和X射线衍射仪分析了压铸态微观组织和相组成,并测试了其拉伸力学性能、硬度、导热性能和流动性能.结果 表明,在AZ91D合金中添加1.11％Nd后,压铸态晶粒有所细化,形成较多弥散分布的细小颗粒状Al2Nd和少量针状Al11N...     

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.     

浇铸温度与模具温度对AZ91D和Mg-3Nd-0.2Zn-Zr镁合金热裂性能的影响(英文)

研究了浇铸温度和模具温度两个温度参数在重力金属型铸造中对商业AZ91D和新型Mg-3Nd-0.2Zn-Zr(质量分数,%;NZ30K)镁合金热裂性能的影响。结果表明,模具温度对合金热裂性能的影响比浇铸温度的更显著,后者的影响仅在模具温度较低时(AZ91D在341 K,NZ30K在423 K)有所显现。与只包含补缩参数的热裂模型相比,同时包含补缩参数、晶粒尺寸和合金凝固区间的热裂模型更能够准确地评价不同镁合金的热裂性能。为了获得较好的热裂抗力,建议AZ91D合金的浇铸温度为961~991 K,模具温度≥641 K;NZ30K合金的浇铸温度为1003~1033 K,模具温度≥623 K。     

Microstructures and mechanical properties of AZ91D/0Cr19Ni9 bimetal composite prepared by liquid-solid compound casting

The liquid-solid compound casting technology was used to produce the AZ91D/0Cr19Ni9 bimetal composite without and with hot dipping aluminium, respectively. The influences of Al coating on microstructures and mechanical properties of AZ91D/0Cr19Ni9 interface were investigated. The results showed that the mechanical bonding was obtained between AZ91D and bare steel 0Cr19Ni9 where a gap existed at the interface; the metallurgical bonding was formed between AZ91D and Al-coated 0Cr19Ni9, which could be divided into two different intermetallic layers: layer I was mainly composed of α-Mg+β-Mg₁₇Al₁₂ eutectic structure and a small amount of MgAl₂O₄, and layer II mainly comprised of Fe₂Al₅ intermetallic compound. Furthermore, the hardness value of interface was obviously higher than that of AZ91D matrix, and the average hardness values of layers I and II were HV 158 and HV 493, respectively. The shear strength of AZ91D/Al-coated 0Cr19Ni9 interface was higher than that of AZ91D/bare 0Cr19Ni9 interface, which confirmed that Al coating could improve the adhesive strength between AZ91D and 0Cr19Ni9 during liquid-solid compound casting process.     

铸造镁合金旋转喷吹除气的试验研究

研究了旋转喷吹技术在AZ91镁合金熔体除气净化处理上的应用。采用减压凝固法考察了旋转喷吹的除气净化工艺的净化效果，确定了最佳的除气时间。利用金相显微镜观察了除气前后合金的微观组织。对除气前后的合金，进行了金属型和低压砂型铸造试验浇注，并对其力学性能进行了测试和比较。研究结果表明，经过30min旋转喷吹除气处理后，能快速显著地降低镁合金中的含气量，AZ91合金金属型和低压砂型试样的力学性能都明显地得到提高，特别是合金的伸长率得到大幅度的提高。     

Ductile Ti-based nanocrystalline matrix composites

High-strength Ti–Nb–Cu–Ni–Al in situ cast composites were prepared via arc-melting and injection casting into a copper mold. The microstructure of the Ti-based alloys consists of a bcc β-Ti type main phase and minor amounts of several nanocrystalline interdendritic phases. The optimization of the Ti-based alloy composition is performed to achieve both high strength and high ductility. The best combination of strength and ductility was found for a copper mold cast (TiNb)₇₉(CuNiAl)₂₁ alloy, which exhibits a fracture strength of more than 2000 MPa coupled with a plastic strain of 30%. Also the arc-melted ingot of this alloy exhibits similar mechanical properties compared to its mold cast counterpart. These features significantly improve the mechanical behavior of such composites and open the possibility of obtaining tailored mechanical properties by controlling composition and solidification conditions.     

工艺参数和热处理对挤压铸造AZ91D力学性能的影响

通过试验研究了工艺参数和热处理对挤压铸造AZ91D合金力学性能的影响。结果表明:合理的工艺参数使AZ91D合金在普通冷室压铸机条件下可以获得良好的力学性能。且经固溶处理后其抗拉强度、硬度和伸长率都会提高,而经固溶时效处理后抗拉强度和硬度会进一步提高,但伸长率有所下降。     

Microstructure and mechanical properties of AZ91-Ca magnesium alloy cast by different processes

The microstructure and mechanical properties of magnesium(Mg) alloys are significantly influenced by the casting process. In this paper, a comparative study on microstructure and mechanical properties at ambient and elevated temperatures of AZ91-2 wt.% Ca(AZX912) Mg alloy samples prepared by gravity casting(GC), squeeze casting(SC) and rheo-squeeze casting(RSC), respectively, was carried out. The results show that α-Mg grains in SC and RSC samples are significantly refined compared to the GC sample. The average secondary dendritic arm spacing of AZX912 alloy samples decreases in the order of GC, SC and RSC. As testing temperature increases from 25 °C to 200 °C, strength of AZX912 alloy samples is reduced, while their elongation is increased continuously. Compared to GC and SC processes, RSC process can improve the mechanical properties of AZX912 alloy at both ambient and elevated temperatures. The enhancement of mechanical properties of RSC sample over GC and SC samples mainly results from grain refinement in the as-cast microstructure of AZX912 alloy.