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.     

热处理和挤压对WE53镁合金组织与力学性能的影响

为提高WE系列生物镁合金的力学性能,采用重力铸造法制备了Mg-5Y-2Nd-1Gd-0.5Zr （质量分数,WE53）镁合金,并对铸态合金进行了固溶处理（T4）,固溶＋时效处理（T6）和挤压加工.利用光学显微镜和扫描电子显微镜观察了合金的显微组织,并利用拉伸试验机和显微硬度计测试了合金室温力学性能.结果表明,铸态合金屈服强度为130 MPa,伸长率为10.2%,T6处理可显著提高铸态合金的强度和硬度,降低合金的伸长率;挤压变形明显提高合金的强度和硬度,伸长率与铸态相当.通过适当的热处理和挤压变形可显著改善WE53镁合金的力学性能.     

Effect of Yttrium and Cerium Addition on Microstructure and Mechanical Properties of AM50 Magnesium Alloy

To develop magnesium alloy with low cost, high strength and excellent elevated temperature properties, effect of Y and Ce addition on microstructure and mechanical properties of AM50 magnesium alloy was studied. Result showed that addition of small amount of Y and Ce to AM50 alloys resulted in refinement of microstructure. Owing to the improvement of microstructure, the mechanical properties of alloys at both ambient and elevated temperature were increased. AM50 alloy containing 0.6 % Ce-0.3 % Y （mass fraction） had good refinement effect and relatively ideal mechanical properties.     

Grain coarsening in semi-solid state and tensile mechanical properties of thixoformed AZ91D-RE

For thixoforming to be possible,the microstructure of the starting material must be non-dendritic,which can be obtained by the strain induced melt activation(SIMA)route.Based on the SIMA route,as-cast AZ91D alloy with the addition of yttrium was deformed by cyclic closed-die forging(CCDF).Microstructure evolution of CCDF formed AZ91D-RE alloy during partial remelting were investigated.Furthermore,the mechanical properties of thixoformed AZ91D-RE magnesium alloy components were also studied.The results showed that prolonged holding time resulted in grain coarsening and the improvement in degree of spheroidization.The coarsening behaviour of solid grains in the semi-solid state obeyed Ostwald ripening mechanism.The coarsening rate constant of CCDF formed AZ91D-RE during partial remelting was 324 um3/s at 550℃.The value of yield strength,ultimate tensile strength and elongation to fracture of four-pass CCDF formed AZ91D-RE magnesium alloy were 214.9,290.5 MPa and 14%,respectively.Then the four-pass CCDF formed alloys were used for thixoforming.After holding at 550℃ for 5 min,the values of yield strength,ultimate tensile strength and elongation to fracture of thixoformed component were 189.6 MPa,274.6 MPa and 12%,respectively.However,prolonged holding time led to remarkable decrease in mechanical properties of thixoformed components.     

Effect of Duplex Ageing on the Properties of A356 Alloy Containing Rare Earth Elements

Reduced weight of automobiles for the purpose of fuel economy has encouraged the use of light metals especially aluminium alloys. A356 Al alloy containing 7% Si and 0.3% Mg is widely used in automobile and aircraft industries due to excellent castability, good corrosion resistance and good pressure tightness. A356 is age hardenable alloy and there is appreciable improvement in strength and hardness achievable due to precipitation of intermetallic compound Mg₂Si. In the present investigation, aluminium alloy A356 with and without rare earth (RE) addition (0.5 wt%) was subjected to single ageing as well as double aging treatment. The results were compared for mechanical properties like hardness and ultimate tensile strength with the material not containing RE additions.     

稀土元素Sm对Mg-Zn-Y合金组织结构和力学性能的影响

制备了Mg-6Zn-1.5Y-0.8Zr-xSm(x=0,1,2,3)系列合金,研究了稀土元素Sm对Mg-6Zn-1.5Y-0.8Zr合金组织结构和力学性能的影响.通过金相显微镜、扫描电镜、EDS、XRD等观察和分析了合金的微观形貌和组织结构,测量了合金抗拉强度、屈服强度和伸长率等力学性能.结果表明:合金中添加稀土元素Sm后晶粒有了明显的细化,随着Sm元素含量的增加,晶粒细化效果更为明显;通过XRD分析,添加Sm元素后,合金中并没有出现新的含Sm的物相,通过扫描电镜和EDS分析表明,合金中加入的Sm置换了部分Y,形成了Mg3( SmY)2 Zn3,Mg3( SmY) Zn6的相结构,Sm元素对Y的置换主要出现在Mg3( SmY) Zn6结构当中,在Mg3 (SmY) Zn6相结构出现较少;力学性能测试结果表明,随着Sm含量增多,合金晶粒细化,细晶强化作用明显,合金屈服强度逐渐增大,而抗拉强度和伸长率在Sm含量为2％时达到最大,比未添加Sm元素时提高约15％以上.     

Study on microstructure and mechanical properties of as-cast Mg-Sn-Nd alloys

Microstructure, tensile properties and compressive creep behaviors of Mg-(1.65-11.52) wt.% Sn-2 wt.% Nd alloys were studied in this paper. The microstructure of the as-cast Mg-Sn-Nd alloys consisted of dendritic α-Mg, Mg2Sn and Mg-Sn-Nd ternary phase containing rare earth element. The highest ultimate tensile strength of 140 MPa and percentage elongation after fracture of 9.7%, were achieved with a composition of Mg-8.23 wt.% Sn-2 wt.% Nd. The compressive creep resistance of Mg-8.23 wt.%Sn-2 wt.% Nd alloy w...     

Effect of Neodymium on As-Cast Microstructure and Mechanical Properties of AZ31 Wrought Alloy

Nd in the form of powder or intermediate alloy was added to AZ31 wrought alloy. The as-obtained alloy was characterized and tested with respect to its microstructure and mechanical properties. The relationship between the microstructure, mechanical properties and tensile fracture mechanism were discussed, with relevant alloys as reference for comparison. Experimental results show that the same quantity of Nd was added into AZ31 in powder form or in intermediate alloy, the absorption rate of Nd reached only 10.8% for the former case and as high as 95% for the later case. Pure Nd powder was added, no new compound was detected, but it served as reductant and purified alloy melt, resulting in improving the tensile strength while Nd was added into AZ31 as Mg-Nd intermediate alloy. The compound Al2Nd and Mg12 Nd were formed in magnesium alloy, which were distributed in the matrix in the shapes of strip and particle, evidently refined the as-cast structure. The as-cast tensile strength (228MPa) of adding pure Nd powder approximated to the figure (245MPa) of adding Mg-Nd intermediate alloy. The tensile fracture mchanism of as-cast AZ31 transformed from cleavage fracture into quasi-cleavage fracture.     

Microstructure and mechanical properties of A356 alloy with yttrium addition processed by hot extrusion

The effects of the rare earth element yttrium(Y) and hot extrusion on the microstructure and mechanical properties of A356 alloy were investigated by mechanical properties testing and microstructure observation. The results indicate that the addition of Y improves the microstructure of the as-cast alloy. The distribution of primary α-Al is uniform and orderly. The long needle-like eutectic Si phases and β-Fe phases turn to strips and short rods. When the content of Y increases to 0.2 wt%, the mean diameter of aAl(40.3 μm) and the aspect ratio of the eutectic Si phase(2.3) reach the minimum values, which are68.9% and 86.1% lower, respectively, than that of the alloy without Y addition. Under extrusion stress, the shape of the eutectic Si phase is changed from long rod-like to near grain-like after solution treatment.The size of the eutectic Si phase is significantly reduced. The needle-like β-Fe phases are squeezed and broken. The mechanical properties of the as-extruded alloy are significantly improved compared to the as-cast alloy. When the rare earth content is 0.2 wt%, the ultimate tensile strength, hardness and elongation of the alloy reach the maximum values, which are 328.2 MPa, 110.4 HV and 21.3%, respectively, and increase by 42.01%, 37.71% and 481.91%, respectively, in comparison to the as-cast alloy without Y addition.     

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。     

Sc对7056铝合金组织和性能的影响

对铸态合金进行了均匀化处理、挤压、固溶处理和时效处理，通过分析合金的化学成分，观察合金在不同状态的显微组织及析出相透射电镜(TEM)形貌，测试合金在热处理后的硬度和拉伸性能，研究了向7056铝合金中加入质量分数0.2%的Sc对合金组织和性能的影响.实验结果表明，Sc元素的加入可以明显细化组织晶粒，铸态晶粒由100~500 μm下降到50 μm左右；Sc元素的加入对合金的塑性有大幅度提高，时效处理后，合金的断后伸长率从10.82%增加到了13.60%；但屈服强度却由668 MPa下降到657 MPa.通过综合计算晶粒大小、析出相强化等因素，详细分析了Sc元素加入引起7056铝合金峰时效态屈服强度下降的原因.理论计算显示，向合金中加入质量分数0.2%的Sc元素时，峰时效处理后，合金的强度值会下降12.005 MPa，与试验值11 MPa接近.研究得到7056铝合金最佳的单级时效制度为120℃+16 h，峰值硬度和强度为195.2 HV和714 MPa，此时合金中主要强化相为圆盘状和短棒状的MgZn₂相，大小约为4~6 nm，同时存在球状的Al₃Zr相，大小约为20 nm.      

Effect of homogenization on microstructure and properties of WE91 alloys

The microstructure and properties of the Mg-9Y-1MM-0.6Zr alloy were studied by scanning electron microscopy, optical microscopy, transmission electron microscopy, hardness and tensile testing. Homogeni...     

Effect of Rare Earth on Microstructure of γ-TiAl Intermetallics

The rare earth (RE) elements (Ce, La) were added to binary Ti-47% Al alloys (atomic fraction) by Induction Skull Melting. The element Ce of 1.0 atomic percent was added individually, and La of 0.2 atomic percent was added individually. This article studied the influences of rare earth metal (Ce, La) on microstructure of as-cast TiA1 based alloy by XRD, SEM, EMPA and TEM measurement methodology. The results show that most of rare earth-rich phases (AlCe, Al-La) are uniformly distributed in grain boundary in the shape of discontinuous network, and some particles of rare earthrich phases within the grains are mainly ellipsoids. In addition, rare earth element can obviously refine the grain size and the lamellar thickness of as-cast TiAl based alloy samples. The grain size of Ti-47Al-1.0Ce-0.2La alloy reaches about 30～80μm, and the lameUar thickness of its γ phase and α2 phase are less than 200 and 20nm, respectively.     

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.     

RE 对 ZnAl4 合金组织和力学性能的影响

在ZnAl4合金中添加RE元素对其进行变质处理,通过金相组织和力学性能分析,研究了RE对该合金的显微组织和力学性能的影响。结果表明,基体中加入适量的稀土后,优化了组织结构,细化了晶粒,使合金的强度、硬度提10%以上,延伸率也有一定的提高。     

稀土对Cu—Ni—Zn合金性能及显微结构的影响

研究了稀土对ＣｕＮｉＺｎ合金机械性能及显微结构的影响。用扫描电镜、金相显微镜及Ｘ射线衍射等方法观察、分析了稀土元素在合金中的分布及作用。试验结果表明,稀土对ＣｕＮｉＺｎ合金机械性能及显微结构均有影响,主要表现在细化铸锭组织及再结晶组织,提高抗拉强度及硬度,而延伸率有所下降;但合金中的稀土添加量不能大于１０％,超过该范围时合金的热塑性变差,难以加工成形     

Influences of Molybdenum and Rare Earth on Mechanical Properties of ZG30Cr

Alloying is an important method to improve properties of casts. The influences of Mo and RE on the mechanical properties of ZG30Cr were investigated in this work. A good comprehensive mechanical properties of the alloy with 0.3% Mo and 0.1% RE were obtained. The elongation, tensile strength, impact toughness and hardness of the alloy reaches 7.21%, 577.49 MPa, 91.7 J·cm-2 and HRC 24.6, respectively.     

稀土Nd对AZ 31镁合金铸态组织和力学性能的影响

利用气氛电阻炉制备了AZ 31-xNd合金(x=0.05%,0.1%,0.2%,0.4%,0.6%),采用光学显微镜(OM)、扫描电子显微镜(SEM)和电子能谱分析仪(EDS)对不同Nd含量的实验合金进行了显微组织观察和分析,结果发现,Nd在AZ 31-xNd合金中形成了Al_3Nd和Mg_(12)Nd相,这些含Nd相导致AZ 31镁合金在凝固过程中的晶粒细化,从而提高了AZ 31镁合金的铸态室温力学性能,随着Nd含量的增加,合金的铸态室温抗拉强度极限和延伸率均先升高后降低.     

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。     

Influence of alloying elements and grain refiner on microstructure,mechanical and wear properties of Mg-Al-Zn alloys

In the present investigation, the effects of alloying elements (Sn, Pb) and grain refiner (Ag, Zr) on microstructure, mechanical and wear properties of as-cast Mg-Al-Zn alloys were studied. The alloys were prepared through melting-casting route under a protective atmosphere and cast into a permanent mould. The microstructure of the base alloy consisted of α-Mg, Mg₁₇Al₁₂ continuous eutectic phase at the grain boundary and Mg-Zn phase was distributed within the grains. Addition of Sn and Pb suppressed the formation of continuous Mg₁₇Al₁₂ eutectic phase and formed Pb enriched Mg₂Sn precipitates at the grain boundary as well as inside the grain. The Ag and Zr addition to Mg-Al-Zn-Sn-Pb alloy suppressed the Mg₁₇Al₁₂ phase formation and refined the grains leading to improve mechanical properties. Addition of Sn, Pb and grain refiner (Ag, Zr) significantly enhanced the tensile strength and elongation but reduced hardness. The Ag addition imparted best tensile properties, where ultimate tensile strength (UTS) and elongation are 205?MPa and 8.0%, respectively. The fracture surfaces were examined under SEM which revealed cleavage facets and dimple formation. Therefore, the cleavage fracture and dimple rupture were considered as the dominant fracture mechanisms for developed Mg alloys. The cumulative volume loss of Mg alloys increased with sliding distance and applied load. The coefficient of friction decreased with sliding distance. The microscopic observation, analysis of the wear surface and coefficient of friction revealed that the wear mechanism of developed Mg alloys changes from abrasion oxidation to delamination wear.