Effects of heat treatments on microstructure and mechanical properties of Mg-15Gd-5Y-0.5Zr alloy

Microstructure and mechanical properties of Mg-15wt.%Gd-5 wt.%Y-0.5wt.% Zr alloy were investigated in a series of conditions. The eutectic was dissolved into the matrix and there was no evident grain growth after solntionized at 525 ℃ for 12 h. The evolution of the phase constituents from as-cast to cast-T4 was as follows： α-Mg solid solution＋Mg5（Gd,Y） entectic compound→α-Mg solid solution＋ spheroidized Mg5（Gd, Y） phase→α-Mg supersaturated solid solution＋cuboid-shaped compound （Mg2Y3Gd2）. And the precipitation sequences of Mg-15Gd-5Y-0.5Zr alloy were observed, according to the hardness response to isothermal ageing at 225-300 ℃ for 0-128 h.     

不同冷速凝固的Mg-9Gd-0.8Al合金固溶行为及组织性能

为了探究Al元素在不同冷却速度下对Mg-9Gd合金组织细化效果及其对后续固溶处理的影响,利用铁模和铜模重力铸造制备了铸态Mg-9Gd-0.8Al合金,之后进行10～50 h的固溶处理。采用OM、SEM、TEM、EDS及XRD等方法研究了冷却速度对Mg-9Gd-0.8Al合金凝固和固溶行为及组织力学性能的影响。结果表明,铁模和铜模制备的铸态Mg-9Gd-0.8Al合金组织均由α-Mg基体、花瓣状(Mg, Al)₃Gd相、细条状Mg₅Gd相和方块状Al₂Gd相组成。铜模相比于铁模冷却速度加快,制备的合金基体晶粒和第二相显著细化,第二相体积分数总量增长幅度达56.1%。2种模具制备的合金固溶10 h后,Mg₅Gd相溶解、(Mg, Al)₃Gd相部分溶解、高熔点Al₂Gd相无变化,晶粒内析出层片状(Mg, Al)₂Gd新相,第二相总量趋于相等。固溶50 h后,(Mg, Al)₂Gd层片相回溶,残余(Mg, Al)     

不同冷速凝固的Mg-9Gd-0.8Al合金固溶行为及组织性能

为了探究Al元素在不同冷却速度下对Mg-9Gd合金组织细化效果及其对后续固溶处理的影响,利用铁模和铜模重力铸造制备了铸态Mg-9Gd-0.8Al合金,之后进行10~50 h的固溶处理。采用OM、SEM、TEM、EDS及XRD等方法研究了冷却速度对Mg-9Gd-0.8Al合金凝固和固溶行为及组织力学性能的影响。结果表明,铁模和铜模制备的铸态Mg-9Gd-0.8Al合金组织均由α-Mg基体、花瓣状(Mg, Al)₃Gd相、细条状Mg₅Gd相和方块状Al₂Gd相组成。铜模相比于铁模冷却速度加快,制备的合金基体晶粒和第二相显著细化,第二相体积分数总量增长幅度达56.1%。2种模具制备的合金固溶10 h后,Mg₅Gd相溶解、(Mg, Al)₃Gd相部分溶解、高熔点Al₂Gd相无变化,晶粒内析出层片状(Mg, Al)₂Gd新相,第二相总量趋于相等。固溶50 h后,(Mg, Al)₂Gd层片相回溶,残余(Mg, Al)₃Gd相发生熔断呈颗粒状,铜模制备的合金第二相颗粒比铁模的更细小。细晶强化和第二相强化使铜模制备的铸态合金性能较铁模制备的合金性能大幅提高,固溶10 h后合金屈服强度提升,伸长率基本不变。固溶处理50 h后,固溶强化、细晶强化和细小颗粒的第二相强化使铜模制备的固溶50 h态合金获得最优性能,屈服强度、抗拉强度和伸长率分别为141 MPa、234 MPa和22.4%。     

Mg-10Gd-4.8Y-0.6Zr合金在520℃下的固溶处理行为

采用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、显微硬度测试、热分析、能谱分析以及X射线衍射(XRD)等手段,研究Mg-10Gd-4.8Y-0.6Zr合金铸态和520℃固溶处理不同时间后的显微组织以及显微硬度分布.结果表明:Mg-10Gd-4.8Y-0.6Zr合金经520℃/16 h固溶处理后,铸态时的...     

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...     

Microstructure and mechanical properties of as-cast and heat treated Mg-15Gd-3Y alloy

The microstructure evolution and mechanical properties of Mg-15Gd-3Y alloy were investigated in the as-cast and heat treated conditions.The microstructure evolution from as-cast to cast-T4 states involved α-Mg solid solution+Mg5(Gd,Y) phase→α-Mg supersatu-rated solid solution+rare earths compound Mg3(Gd1.26,Y0.74)→α-Mg supersaturated solid solution+rare earths compound Mg3(Gd0.745,Y1.255).It showed that 480 oC/4 h was the optimal solution treatment parameter.If the solution temperature was high or the holding time was long,such as 520 oC/16 h,an overheating phenomenon would be induced,which had a detrimental effect on the mechanical properties.When age-ing at 225 and 200 oC,the alloy would exhibit a significant age-hardening response and great long-time-age-hardening potential,respectively.The best mechanical properties were obtained at the parameters of 480 oC/4 h+225 oC/16 h,with the UTS of 257.0 MPa and elongation of 3.8%.     

Microstructure and mechanical properties of Mg-10Y-2.5Sm alloy

The microstructure and mechanical properties of aged Mg-10Y-2.5Sm alloy were investigated.The results showed that the microstructure of the alloy consisted of α-Mg matrix and Mg24Y5 phase,and fine Mg24Y5 particles distributed in α-Mg matrix uniformly and dispersedly.Sm enhanced α-Mg matrix and Mg24Y5 phase by solid solution effect.At 200-300 oC,the ultimate tensile strengths were more than 200 MPa and the elongations were about 3%.Compared with those at room temperature,the mechanical properties had no obvious changes.     

Sr对Mg-5Sn-5Zn铸造镁合金组织的影响

通过光学显微镜、扫描电镜和X射线衍射仪研究了Mg - 5Sn - 5Zn - xSr(x=0,0.5,1,2)4种铸造镁合金的显微组织和相组成.结果表明:在Mg -5Sn -5Zn合金中加入质量分数为0.5％ ～2％的Sr元素后,不但能够缩小α - Mg枝晶间距,而且还能形成三元相MgSnSr.随着Sr含量的增加,在晶界析出的Mg2Sn相减少,晶内的MgSnSr相增加.合金中的MgZn相与Mg2Sn相依附在一起,大多数的MvgZn相以α-Mg+ MgZn相的共晶方式存在.     

Microstructure and mechanical properties of Mg-Zn-Y-Nd-Zr alloys

The microstructure and tensile properties of the as-cast and solution treatment Mg-4.5Zn-1Y-xNd-0.5Zr (x=0, 1 wt.%, 2 wt.%, 3 wt.%) alloys were investigated. The results showed that the microstructure of Mg-4.5Zn-1Y-0.5Zr alloy consisted of α-Mg, Zn-Zr, W (Mg₃Y₂Zn₃) and I (Mg₃YZn₆) phases. With the addition of Nd, I-phase disappeared and Mg₃Y₂Zn₃ phase changed into Mg₃(Nd,Y)₂Zn₃ phase. When the content of Nd reached 3 wt.%, T phase, i.e., ternary Mg-Zn-Nd phase, formed. In addition, with the increase of Nd content in the alloys, the secondary dendritic arm spacing decreased, while the amount of intermetallic phases increased. For as-cast Mg-4.5Zn-1Y-xNd-0.5Zr alloys, after solution treatment, microsegregation was eliminated and the shape of eutectic structure of α-Mg+W transformed from lamellar into spherical. The tensile strength and elongation of Mg-4.5Zn-1Y- 3Nd-0.5Zr alloy were increased from 219.2 MPa and 11.0% to 247.5 MPa and 20.0%, respectively.     

Microstructure and mechanical properties of Mg-Gd-Y-Sm-Al alloy and analysis of grain refinement and strengthening mechanism

The effects of Sm on the microstructure and mechanical properties of Mg-11 Gd-2 Y-0.6 Al alloy were investigated by X-ray diffraction,optical microscopy,scanning electron microscopy,energy dispersive spectrometry and high resolution transmission electron microscopy.Based on the theory of edge—edge matching and electronegativity theory,the mechanism of grain refinement is discussed.The strengthening mechanism is expounded conveniently from fine grain strengthening,coherent strengthening,precipitation strengthening and grain boundary strengthening.The results show that the micro structure of Mg-11 Gd-2 Y-0.6 Al alloy is mainly composed of a-Mg matrix,Mg_5 Gd and Mg_(24)Y_5 phases.The addition of Sm forms Mg_(41)Sm_5 phase in the alloy and refines the alloy.The addition of Sm significantly improves the mechanical properties of the alloy at room and high temperatures.When the addition of Sm is 3 wt%,the tensile strengths of the alloy at room temperature and high temperature(200℃) reach the maximum value 292 and 321 MPa,respectively.The fracture mode of the alloy at different temperatures is mainly brittle fracture and intercrystalline fracture.     

Microstructure and mechanical properties of Mg-10Y-2.5Sm alloy

The microstructure and mechanical properties of aged Mg-10Y-2.5Sm alloy were investigated. The results showed that the microstructure of the alloy consisted of α-Mg matrix and Mg₂₄Y₅ phase, and fine Mg₂₄Y₅ particles distributed in a-Mg matrix uniformly and dispersedly. Sm enhanced α-Mg matrix and Mg₂₄Y₅ phase by solid solution effect. At 200-300 °C, the ultimate tensile strengths were more than 200 MPa and the elongations were about 3%. Compared with those at room temperature, the mechanical properties had no obvious changes.     

Mg-5Gd-3Y-0.8Zr合金的微观组织及耐NaCl溶液腐蚀性能研究

系统研究了Mg-5Gd-3Y-0.8Zr合金的微观组织和耐蚀性能,通过静态失重法测定了其在NaCl溶液中的腐蚀速率。结果表明:铸态合金主要由基体α-Mg和方块状β相(Mg_5Gd、Mg_(24)Y_5)组成,时效处理后分布在晶界处的共晶β相数量明显增加;在NaCl溶液中腐蚀12 h以后镁合金的腐蚀速率明显增加,在3.5%Na Cl(质量分数)溶液中腐蚀24 h后,镁合金已被严重腐蚀,表面布满腐蚀坑和未脱落的白色腐蚀产物;镁合金易产生沿晶腐蚀,方块状共晶β相颗粒可有效阻止表面腐蚀沿晶界向镁合金内部扩展,从而提高镁合金的耐蚀性。     

Effect of Yttrium on Microstructures and Properties at Elevated Temperature of Mg-0.8Zr-0.35Zn Alloys

Asthelighteststructuralmetalmaterial ,themostobviousadvantagesofmagnesiumalloyaretheirhighspecificstrengthandspecificstiffness ,superdampingcapacityandmachinability ,excellentelectromagneticshieldingandnon toxicity .Theincreasingattentionhasbeenpaidonthepracticalapplicationofmagne siumalloysastheenergysavingandenvironmentpro tectionarebecomingtheworldfocus .However ,somedisadvantagessuchasignitableandcombustibledur ingmeltingandcastingandtheirrelativelypoorprop ertiesatelevatedtemperaturelimit…     

Influence of Al-Si additions on mechanical properties and corrosion resistance of Mg-8Li dual-phase alloys

Sheet samples of Mg-8Li,Mg-8Li-3Al,Mg-8Li-3AlSi and Mg-8Li-5AlSi alloys were obtained by hot rolling.Optical microscope,microhardness tester,nanoindentor,X-ray diffractometer and electrochemical analyzer were adopted to investigate the microstructures,micro-mechanical properties and corrosion resistance.Roller was preheated to 150°C before rolling process,and rolling reduction designed was about20% per pass with a total rolling reduction of 84%.The rolled plates were annealed at 200°C for 120 min.The tensile tests were performed at room temperature.Experimental results showed that both the strength and corrosion resistance of theα+βdual-phase of Mg-Li alloy were significantly improved with adding Al-Si elements.The strength enhancement was attributed to the solid solution of Al into theα-Mg matrix and into theβ-Li matrix as well as to the precipitation strengthening of Mg2 Si particles.Besides,the dendrite grains ofα-Mg transformed to equiaxed ones with addition of Al into alloy Mg-Li.     

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...     

Homogenization heat treatment of Mg-7.68Gd-4.88Y-1.32Nd-0.63Al-0.05Zr alloy

The microstructures and mechanical properties of the Mg-7.68Gd-4.88Y-1.32Nd-0.63A1-0.05Zr magnesium alloy were investigated both in the as-cast condition and after homogenization heat treatment from 535 to 555 ℃ in the time range 0-48 h by op- tical microscopy, scanning electron microscopy and hardness measurement. The as-cast alloy consisted of ct-Mg matrix, Mgs（Y0.5Gd0.5） phase which is a eutectic phase, strip of Al2（Y0.6Gd0.4） phase, little A13Zr and Mg（Y3Gd） phase. With the increasing of homogenization temperature and time, the Mgs（Y0.5Gd0.5） phase was completely dissolved into the matrix. The Al2（Y0.6Gd0.4） phase was almost not dissolved which impeded grain boundaries motion making the grain size almost not changed in the process of ho- mogenization. The optimum homogenization condition was 545 ℃/16 h. The tensile strength increased, yield strength decreased and the plasticity improved obviously after 545 ℃/16 h homogenization treatment.     

The microstructural development of Mg-9 pct Al-1 pct Zn alloy during injection molding

Ex-situ microstructural analysis was used in order to assess the high-temperature transformations of the Mg-9 pct Al-1 pct Zn alloy within the injection-molding system. In addition to as-cast ingot, chipped feedstock, and final products, the alloy samples at different stages of the process were investigated. It was revealed that the cold deformation during ingot chipping and recrystallization during initial stages of residency inside the barrel led to nucleation and growth of the equiaxed grain structure. Subsequent melting of the Al-rich phase followed by liquid-alloy wetting of α-Mg grain boundaries initiated the formation of the slurry with globular solid particles. The structural evolution of the semisolid alloy under the simultaneous influence of temperature gradient and injection-screw shear is considered, and the mechanisms involved are discussed. It is concluded that during processing of partially remelted alloy the temperature profile along the injection-molding barrel in combination with the feedstock structure are key factors that control both the transformation of the thixotropic slurry and the final morphology of the primary solid phase.     

Effect of Gd on microstructure,mechanical properties and wear behavior of as-cast Mg–5Sn alloy

Effect of minor Gd addition on the microstructure, mechanical properties and wear behavior of as-cast Mg–5Sn-based alloy was investigated by means of OM, XRD, SEM, EDS, a super depth-of-field 3D system, standard high-temperature tensile testing and dry sliding wear testing. Minor Gd addition has strong effect on changing the morphology of the Mg–5Sn binary alloy. Gd addition benefits the grain refinement of the primary α-Mg phase, as well as the formation and homogeneous distribution of the secondary Mg₂Sn phase. The mechanical properties of the Mg–5Sn alloys at ambient and elevated temperatures are significantly enhanced by Gd addition. The wear behavior of the Mg–5Sn alloy is also improved with minor Gd addition. The alloy with 0.8% Gd addition exhibits the best ultimate tensile strength and elongation as well as the optimal wear behavior. Additionally, the worn surface of the Mg–5Sn–Gd becomes smoother in higher Gd-containing alloys. The best wear behavior of alloy was exhibited when Gd addition was up to 0.8%, showing a much smoother worn surface than that of control sample. The improvement of tensile properties is mainly attributed to the refinement of microstructure and the increasing amount and uniform distribution of Mg₂Sn phase. The larger amount of Mg₂Sn phase uniformly distributed at the grain boundary of Mg–Sn–Gd alloys act as a lubrication during sliding, and combined with smaller grain size improve wear behavior of the binary alloy.     

Stable icosahedral phase in Mg_（44）Zn_（44）Gd_（12） alloy

The microstructure of the as-cast Mg 44 Zn 44 Gd 12 alloy was investigated by using X-ray diffraction(XRD),differentical scanning(DSC),scanning electron microscopy(SEM) and a detailed transmission electron microscope.The XRD,DSC and SEM results indicated that the as-cast Mg 44 Zn 44 Gd 12 alloy were mainly composed of three types of phases:the primary solidification phase,the dendritic phase and the eutectic phase.The primary solidification phase had an icosahedral structure.The dendritic phase was the W-phase,and eutectic structure phase was the Mg 7 Zn 3 phase.Microstructures of icosahedral phase(I-phase),W-phase and Mg 7 Zn 3 phase in Mg 44 Zn 44 Gd 12 alloy were investigated.The results indicated that the I-phase in Mg 44 Zn 44 Gd 12 alloy was a face-centered icosahedral quasicrystal with stoichiometric composition of Mg 42 Zn 50 Gd 8 which had an excellent thermal stability up to 420 °C.The solid solution of the Gd gradually decreased during solidification,which played an important role in activating the formation of Mg 7 Zn 3 phase and W-phase from icosahedral phases.     

Microstructure and mechanical properties of RS NiCrAl melt-spun alloys

The microstructure and mechanical properties of three melt-spun NiCrAl alloy ribbons have been studied in the as-cast condition as well as after thermal treatments. The microstructure of the alloys is dendritic-microcellular in as-cast condition and phases present for 10 at.% Al and 30 at.% Al alloys are as is predicted by the equilibrium phase diagram. In the 20 at.% Al alloy, γ' has frozen in metastable form and partial ordering takes place during cooling in the solid state. After thermal treatments the ribbons generally maintain a refined microstructure; α phase precipitates are always found in β and γ' phases in 20 and 30 at.% Al alloys. The hardness of the alloys increases with aluminum content. The tensile strength at room temperature is related to the phases present in the material for each state of treatment. The alloys are brittle, a higher ductility always being obtained in the as-cast condition.