稀土元素铈对镁合金AZ91D显微组织和力学性能的影响

利用光学显微镜、X射线衍射和扫描电镜等分析研究含铈镁合金AZ91D（0．25％Ce、0．7％Ce、0．95％Ce）的显微组织,并对其力学性能进行了测试,同时与不含铈镁合金AZ91D进行了比较。结果表明,加入一定量Ce后的镁合金AZ91D形成杆状化合物Al4Ce,被推移到生长界面,阻碍枝晶的自由生长,从而细化合金显微组织;Ce能提高镁合金AZ91D抗拉强度和硬度,而对其屈服强度和延伸率影响不大;加入0．7％Ce的AZ91D镁合金晶粒细化效果和综合力学性能比较理想。     

稀土熔盐扩渗对AZ91D镁合金耐蚀性能的影响

为了提高镁合金的耐蚀性能,首先采用表面机械研磨的方法实现了AZ91D镁合金表面纳米化,然后研究了Ce、Nd、Y熔盐扩渗对AZ91D镁合金表层组织及耐蚀性能的影响。采用扫描电镜(SEM)、透射电镜(TEM)以及X射线衍射(XRD)对扩渗层形貌及物相进行了表征,并利用电化学工作站测试了稀土扩渗后合金在3.5%NaCl水溶液中的极化曲线。研究结果表明,经过表面纳米化及熔盐扩渗稀土后,AZ91D镁合金表面形成一层均匀、致密的稀土扩渗层,合金耐蚀能力明显提高,腐蚀电流密度降低一个数量级,渗层厚度随着扩渗时间的延长而增加,扩渗层变得更连续、致密,XRD及TEM结果表明,扩渗层主要由α-Mg,Mg_(17)Al_(12)和富稀土相Al2RE(Ce/Nd/Y)组成。     

AZ91D镁合金半固态浆料制备过程中的组织演变

对AZ91D镁合金进行了半固态等温热处理,通过光学显微镜、扫描电镜对其组织进行了研究。结果表明,AZ91D镁合金铸件经过580℃×30min半固态等温热处理后,合金显微组织中β-Mg17Al12相基本熔入基体,枝晶状的铸态组织在等温处理过程中变得细小圆整。     

铈对铸造镁合金AZ91D显微组织与力学性能的影响

利用光学金相显微镜OM和XRD分析了分别加入0．1％，0．3％，0．5％，0．7％和1．0％Ce的AZ91D合金显微组织和相组成，测试了室温力学性能和硬度。结果表明，加入一定量Ce后的AZ91D合金形成杆状化合物Al4Ce，被推移到生长界面，阻碍枝晶的自由生长，从而细化合金显微组织；Ce能提高AZ91D合金室温抗拉强度和硬度，而对其屈服强度和延伸率影响不大；加入0．7％Ce的AZ91D合金晶粒细化效果好，其综合力学性能比较理想。     

Er对AZ91镁合金铸态组织和耐蚀性能的影响

利用真空电磁感应熔炼炉制备AZ91-XEr(X=0,0.58%,1.14%,1.81%)镁合金,采用静态失重法测试实验合金腐蚀行为,运用金相显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)等测试手段对腐蚀前后实验合金进行表征,研究Er对实验合金显微组织及耐蚀性能的影响。结果表明,添加Er后合金组织得到细化,合金物相主要由α-Mg、β(Mg17Al12)和Al2Er相组成。随着Er含量增加,β相由粗大的不连续网状变为细小的块状,且Al2Er相数量、尺寸增加。Er可以提高AZ91镁合金的耐蚀性能,当Er含量为1.81%时,实验合金耐蚀性最好。     

均匀化过程中AZ151镁合金过烧组织的研究

本文以AZ151镁合金作为研究对象,采用X射线衍射分析(XRD)、能谱分析(EDS)和光学显微镜(OM)等手段分析了AZ151镁合金铸态、均匀化态和过烧态的组织和成份组成,研究结果表明,铸态AZ151镁合金由α-Mg基体和β-Mg17Al12相组成,均匀化处理后β-Mg17Al12相含量降低,即使过烧β-Mg17Al12相也不能完全分解,过烧AZ151镁合金组织中出现三个特征:复熔球、复熔晶界和三角晶界。     

超声处理对含稀土的AZ91镁合金性能及组织的影响

在AZ91镁合金熔炼过程中加入混合稀土Y,Gd并辅以超声熔体处理工艺制备合金,利用万能试验机、光学显微镜(OM)和透射电镜(TEM),探讨了添加混合稀土和超声波处理对AZ91镁合金微观组织和力学性能的影响,分析了其作用机制。实验结果表明,添加混合稀土Y,Gd后,未经超声处理的合金,稀土化合物存在于合金晶内和晶界上,α-Mg基体组织得到细化,晶界上的β相减少,合金的抗拉强度σb和延伸率δ可分别达到261 MPa和4.5%。同时,施加超声处理能进一步细化合金组织,α-Mg基体晶粒更加等轴细小,抑制β相在晶界处的连续网状分布。稀土相趋于弥散均匀分布,促进了稀土元素的细晶强化作用,这样使合金抗拉强度提高到270 MPa,延伸率达到7.2%。当混合稀土添加总量超过一定范围后,会形成粗大化合物并割裂基体,这时超声处理对合金组织的改善作用有限,合金力学性能呈现下降趋势。     

熔剂FHRJ对含铈AZ91D镁合金组织和性能的影响

通过对传统熔剂RJ-2和自制熔剂FHRJ对含铈AZ91D镁合金的显微组织和力学性能的研究对比,表明:含铈AZ91D镁合金采用自制熔剂FHRJ熔炼后,Mg17Al12相得到改善,晶内出现Al4C3形核质点,晶粒更细小,合金的抗拉强度、屈服强度及延伸率等力学性能也比传统覆盖熔剂RJ-2更好。     

旋转磁场对富铈混合稀土合金化压铸AZ81镁合金组织与性能的影响

采用自行开发的电磁搅拌器研究了熔炼时向AZ81镁合金中添加富铈混合稀土(MM),同时施加旋转磁场情况下,旋转磁场对MM合金化AZ81镁合金组织和结构的影响。结果表明,随着旋转磁场激磁电压的增大,β-Mg17Al12相的尺寸减小,且分布越来越均匀。室温拉伸试验结果表明施加旋转磁场后,合金的强度、硬度等力学性能增加。蠕变试验结果表明,激磁电压越高,在120 h内合金的总蠕变量越小,其变形率越小。     

热处理对挤压态AZ61-x%La镁合金组织和性能的影响

采用光学显微镜、扫描电镜(SEM)、X射线衍射(XRD)及拉伸实验等方法研究了热处理对挤压态AZ61-x%La镁合金显微组织和力学性能的影响。结果表明,经过T6处理后,原来弥散分布于晶界周围的β-Mg17Al12相经历了从完全溶解到重新析出的过程,并重新分布于晶界周围;β-Mg17Al12相由铸态的网状结构变成块状结构。在晶内一部分区域也出现了小块状的β相。合金中的稀土相能细化晶粒,显著提高合金的硬度。经过T6处理之后合金的抗拉强度,屈服强度和伸长率都有提高,但硬度略有下降。T5处理对合金的力学性能影响不大。     

Effect of mischmetal on mechanical properties and microstructure of die-cast magnesium alloy AZ91D

Effects of the mischmetal addition in range of 0.4 wt.% to 1.7 wt.% on the microstructure and mechanical properties of die-cast magnesium AZ91D were investigated to improve the elevated temperature mechanical properties of the alloy by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and tensile tests. The results revealed that mechanical properties of die-cast magnesium alloy AZ91D-0.4%MM at 100 oC were near to those of die-cast magnesium alloy AZ91D. The ultimate tensile strength, 0.2% proof yield strength and elongation to failure of die-cast magnesium alloy AZ91D at 170 oC were 178, 129 MPa and 20%, respectively. In comparison, the ultimate tensile strength, 0.2% proof yield strength and elongation to failure of die-cast magnesium alloy AZ91D-0.4%MM at 170 oC reached to 206, 142 MPa and 26%, respectively increased by 15.7%, 10% and 30%. Proper addition of mischmetal could enhance the mechanical properties at an elevated temperature, which was attributed to the formation of Al-RE phases with high thermal stability. Hence sliding of grain boundaries and cracks could be effectively hindered by Al-RE phases.     

Fabrication of a novel Mg-RE(Nd,Ce) intermetallic compound coating by molten salt diffusion and its effect on corrosion resistance of magnesium alloys

A novel Mg-rare earth(Nd,Ce) coating containing intermetallic compound was fabricated on the surface of the AZ91D magnesium alloy by bathing the sample in a NaCl-KCl-LiCl-NdCl_3-CeCl_3 molten salt. The cross-sectional morphology, microstructure and phase composition of the coating were investigated by scanning electron microscopy(SEM), transmission electron microscopy(TEM) and energy dispersive spectroscopy(EDS). The corrosion resistance was characterized by the potentiodynamic polarization curves. The SEM observation indicated that a continuous and compact diffusion coating was obtained on the surface of SMATed AZ91D magnesium alloy and the XRD and TEM investigations revealed that the new phases were Al_2Ce and Al_2Nd intermetallic. The potentiodynamic polarization curves showed that the Mg-RE coating improved the corrosion resistance of the AZ91D magnesium alloy, and the corrosion current density of the coated sample was about 1510 mA /cm~2 lower than the uncoated sample.     

High Cycle Fatigue Properties of Die-Cast Magnesium Alloy AZ91D with Addition of Different Concentrations of Cerium

Recently , magnesiumalloy has become a very at-tractive material because of its lowdensity ,high spe-cific strength, and easy recyclability compared withother metals[1].As alight structural material ,recentlythere has been a significantincreaseinthe use of mag-nesiumalloy for automobiles ,aerospace components ,computers , mobile phones , and household equip-ments[2 ,3]. Mg-Al-Zn (AZ91D) alloyis the most wide-ly used die-cast magnesiumalloyin automotive applica-tions due toits excellent casta…     

Effect of Ca and Rare Earth Elements on Impression Creep Properties of AZ91 Magnesium Alloy

Creep properties of AZ91 magnesium alloy and AZRC91 (AZ91 + 1 wt pct RE + 1.2 wt pct Ca) alloy were investigated using the impression creep method. It was shown that the creep properties of AZ91 alloy are significantly improved by adding Ca and rare earth (RE) elements. The improvement in creep resistance is mainly attributed to the reduction in the amount and continuity of eutectic β(Mg₁₇Al₁₂) phase as well as the formation of new Al₁₁RE₃ and Al₂Ca intermetallic compounds at interdendritic regions. It was found that the stress exponent of minimum creep rate, n, varies between 5.69 and 6 for AZ91 alloy and varies between 5.81 and 6.46 for AZRC91 alloy. Activation energies of 120.9 ± 8.9 kJ/mol and 100.6 ± 7.1 kJ/mol were obtained for AZ91 and AZRC91 alloys, respectively. It was shown that the lattice and pipe-diffusion-controlled dislocation climb are the dominant creep mechanisms for AZ91 and AZRC91 alloys, respectively. The constitutive equations, correlating the minimum creep rate with temperature and stress, were also developed for both alloys.     

Study on Ignition Proof AZ91D Magnesium Alloy Chips with Cerium Addition

The effect of Ce on ignition point of AZ91D magnesium alloy chips was studied. For the AZ91D and the AZ91D-xCe magnesium alloys, changing the sizes of the chips in the range of 58 - 270 μm has a limited influence on ignition point, however, the shift of the content of Ce has much effect on ignition point. Increasing the Ce content, x from 0.15 to 0.25, the ignition point increases with increasing of Ce; however, x from 0.25 to 0.45, the ignition point decreases with increasing of Ce. By the addition of Ce of 0.25 %. the ignition point is raised by 43℃.     

Mg-6Al-1Zn-Y镁合金组织及力学性能的研究

在Mg-6Al-1Zn合金的基础上添加不同质量分数的Y（分别为0％，0．5％，0．9％，1．4％），制备了4种实验合金，研究了Y的添加对合金组织性能的影响。通过X射线衍射、金相显微镜、扫描电镜、电子探针等手段分析了Mg-6Al-1Zn合金添加Y后组织结构的变化。研究结果表明，添加了不同含量Y的合金中都出现了一种新相Al2Y相。随着Y含量的增加，Al2Y相数量增多而Mg17Al 12相则减少。Y能细化合金铸态及挤压态显微组织，其细化作用在添加了0．9％Y的镁合金中尤为明显。铸态合金室温拉伸试验表明：该合金具有最佳的综合力学性能。当Y含量添加至1．4％时，Al2Y相变得粗大且出现团聚现象而导致了拉伸性能的下降。经过挤压后，合金的力学性能大幅度上升。     

Corrosion fatigue of die-cast and extruded magnesium alloys

To study the fatigue life of die-cast and extruded AZ91D, AM50 and AZ31 magnesium alloys, corrosion fatigue tests were carried out using a rotating beam type fatigue machine. Corrosive environment (3.5% NaCl) significantly decreases fatigue life of alloys, especially for extruded alloys. The fatigue data at high stresses were analyzed using fitting equations. Extruded alloys show a higher sensitivity to the action of NaCl solution in comparison with die-cast alloys; however, their corrosion fatigue life is longer than that of die-cast alloys. Corrosion fatigue behavior of Mg alloys correlates with their mechanochemical behavior. The latter was studied by the polarization measurements of the dissolution rate of strained alloys. TEM observations confirmed that the maximums on the curves of Mg dissolution rate dependence on the strain in NaCl solution appeared at the work-hardening stages due to the creation and destruction of dislocation pile-ups.     

Microstructure and properties of blended Mg−Al alloys fabricated by semisolid processing

A new procedure for blending die-cast Mg−Al alloys by semisolid processing to achieve controlled variations in microstructure and properties has been investigated. Granules of AM6-B and AZ91D have been blended in varying proportions and Thixomolded at nominal solid fractions of 0.1 and 0.3, respectively. As-molded microstructures and the role of interdifussion during processing have been analyzed in detail by scanning electron microscopy, transmission electron microscopy, and electron microprobe analysis. Tensile properties and failure modes have been analyzed and a strength model that considers solid solution strengthening of Al in the unmelted particles and a rule-of-mixtures behavior for microstructural components is proposed.