双级时效热处理ZM5合金的显微组织和力学性能

以ZM5合金为研究对象,通过显微组织分析和力学性能测试等手段,研究了其不同状态的显微组织和力学性能。结果表明,铸态ZM5合金中存在呈网状分布的粗大不规则块状β-Mg₁₇Al₁₂相;固溶处理后,β-Mg₁₇Al₁₂相溶入α-Mg基体中,仅有少量残余的AlMn相;经T6处理后,沿晶界析出片层状β-Mg₁₇Al₁₂相;经双级时效处理后,沿晶界析出片层状β-Mg₁₇Al₁₂相及在晶内析出细小的针片状β-Mg₁₇Al₁₂相。与铸态相比,热处理后ZM5合金的抗拉强度大幅提升;经双级时效处理后,其抗拉强度可达285MPa,比T6处理后的抗拉强度高20MPa。     

汽车发动机用AZ91D合金的表面喷涂与性能

采用热喷涂工艺在压铸态AZ91D合金表面制备了Al涂层,研究了热处理温度和保温时间对AZ91/Al涂层界面组织形貌的影响,并对比分析了扩散层的耐腐蚀性能和耐磨性能。结果表明,热处理前Al涂层与基材为机械结合,热处理后Al涂层与AZ91合金基材的界面处可形成冶金结合扩散层,且随着保温时间延长,扩散层厚度不断增加;热处理温度在375 ℃以下时扩散层主要由β-Mg₁₇Al₁₂相构成,375 ℃×8 h热处理后为α-Mg+β-Mg₁₇Al₁₂相,425 ℃×1 h热处理后为γ-Mg₂Al₃和β-Mg₁₇Al₁₂相。AZ91合金基材和扩散层腐蚀电位从高至低顺序为γ>β>α+β>AZ91合金基材,扩散层的腐蚀电流密度均低于AZ91合金基材,阻抗谱图中容抗弧半径从大至小顺序为γ>β>α+β>AZ91合金基材,扩散层的耐腐蚀性能均优于AZ91合金基材;γ、β和α+β扩散层的摩擦稳定性系数都高于AZ91合金基材,而磨损速率和磨痕宽度都要小于AZ91合金基材,其中β扩散层的磨损速率和磨痕宽度最小,具有最佳的抵抗磨损的能力。     

添加VN颗粒的铸态AZ91镁合金在NaCl溶液中的腐蚀行为（英文）

采用光学显微镜(OM)、X射线衍射(XRD)、扫描电子显微镜(SEM)技术和电化学实验研究铸态AZ91-xVN(x=0,0.25,0.5,1，质量分数，%)合金的显微组织和腐蚀行为。结果表明，VN对AZ91合金显微组织具有明显的细化和改性作用。随着VN颗粒的加入，AZ91合金的耐腐蚀性能先提高后降低。铸态AZ91-0.25VN合金具有最佳的耐腐蚀性能，其腐蚀速率最低(P_W=(1.47±0.06)mm/a)，这主要归因于其具有更多可作为腐蚀屏障的晶界。随着VN含量的进一步增加，合金中片状β-Mg₁₇Al₁₂析出相的量增加，由于β相与α-Mg基体易发生电偶腐蚀，合金的耐蚀性能逐渐降低。     

Al含量对含稀土AZ系镁合金组织及性能的影响

以含稀土AZ系镁合金为基,制备了铝含量分别为5%、7%、9%的合金试样,并对其进行435 ℃×24 h固溶+200 ℃×24 h时效处理,对试样的铸态、固溶态和时效态的显微组织进行了观察,随后测定了试样时效后的力学性能以及耐蚀性能。结果表明,铸态镁合金组织主要为α-Mg+β-Mg₁₇Al₁₂+Al₁₁(La,Ce)₃和(La,Ce)Al₄;随着Al含量的增加,β-Mg₁₇Al₁₂和稀土化合物相增多,晶粒细化。固溶处理后,组织中的β-Mg₁₇Al₁₂相会逐渐溶解,随着Al含量的增多,溶解将会不完全,未溶的强化相β-Mg₁₇Al₁₂和稀土化合物相弥散分布在晶界及其附近处。时效处理后,随着Al含量的增加,组织中继续析出的β-Mg₁₇Al₁₂相增多,稀土化合物相尺寸细化。随着Al元素的增多,试样的抗拉强度和硬度逐渐增大,塑韧性则愈来愈差,耐腐蚀性越来越好。     

微观组织对AZ系铸造镁合金的腐蚀行为影响研究

耐腐蚀性能的提升有助于轻量化镁合金材料的进一步广泛应用。本文以AZ41和AZ91两种铸造镁合金为研究对象，采用XRD、OM、SEM、EPMA等手段表征分析微观组织，利用EIS测试了两种Mg-Al-Zn合金在0.1 M的Na Cl溶液中的耐蚀性能，结合宏微观腐蚀形貌探讨了微观组织对腐蚀行为的影响机制。研究结果表明，与AZ41合金相比，浸泡初期AZ91合金表面的氧化膜相对完整且化学稳定性更高，在腐蚀初期起到保护作用，AZ91合金浸泡初期的耐蚀性能优于AZ41合金；随浸泡时间延长，AZ41合金中连续网状的过饱和α-Mg+β-Mg₁₇Al₁₂共晶组织阻碍合金的腐蚀扩展；而AZ91合金中不连通的离异共晶β-Mg₁₇Al₁₂相与α-Mg基体耦合，造成明显的局部腐蚀现象。     

固溶冷却方式对AM50镁合金组织和耐蚀性能的影响

通过XRD、SEM、EDS、电化学腐蚀测试,研究了铸造AM50镁合金固溶后水冷和炉冷两种处理方式对组织及耐蚀性能的影响。结果表明,固溶处理后,由于大量Al固溶进α-Mg中,两种方式冷却的AM50镁合金相组成主要为α-Mg、Al₆Mn和少量β-Mg₁₇Al₁₂。由于冷却速率的不同,炉冷样比水冷样的β-Mg₁₇Al₁₂的数量多,体积大,并且围绕Al₆Mn相析出,而且大多在晶界处析出。由极化曲线和腐蚀速率曲线可以看出炉冷样的腐蚀速率较高,耐蚀性较差。由于β-Mg₁₇Al₁₂数量的增加以及α-Mg相中固溶Al的数量减少,导致炉冷试样比水冷试样的腐蚀速率高,而且经过168 h腐蚀形成了蚀坑带。     

La-Ce混合稀土对AZ91D合金组织和性能的影响

以AZ91D镁合金作为研究对象,探究了La-Ce混合稀土含量对其组织性能的影响。结果表明:在AZ91D镁合金中加入混合稀土La-Ce后,铸态组织为网状β-Mg₁₇Al₁₂相及少量杆状稀土化合物。且随着稀土含量增多,β-Mg₁₇Al₁₂和杆状稀土化合物被细化。经固溶时效处理后,随稀土含量增加,试验合金伸长率增大,硬度和抗拉强度均先增后降,稀土含量为2.38%时,合金力学性能最佳。     

固溶处理对半固态注射成形Mg-Al-Zn合金组织及性能的影响

采用注射成形法制备了AZ91D合金试样,利用扫描电镜(SEM)、X射线衍射(XRD)和拉伸试验等研究固溶处理对试样的显微组织、相组成和力学性能的影响。结果表明：镁合金试样经不同温度固溶处理8 h后,其抗拉强度和伸长率先升高后降低,在390℃固溶处理8 h后达到最大值,分别为164.48 MPa和18.55%。根据显微组织观察与XRD分析结果,合金组织中存在片状分布的Mg₁₇Al₁₂相,随固溶时间的增加,Mg₁₇Al₁₂相溶入基体。经390℃固溶处理8 h后,Mg₁₇Al₁₂相溶入合金基体且晶粒无明显长大,固溶效果较佳。     

固溶处理对Mg-6Al-3Zn-0.25Mn合金组织和性能影响

研究了固溶处理对Mg-6Al-3Zn-0.25Mn铸造镁合金显微组织和力学性能的影响。结果表明，铸态和固溶态组织主要由α-Mg基体和Mg₁₇Al₁₂相组成，经过400、410和420℃保温18 h固溶处理后，第二相的种类没有发生变化，大量的Mg₁₇Al₁₂相溶入到α-Mg基体中，合金组织中残留了少量颗粒状Al₄Mn相，同时也出现了梅花状Mg₁₇Al₁₂相。此外，合金经400℃×18 h处理后，晶粒细化程度最好，且表面清晰平整无缺陷，其室温力学性能得到了明显改善，抗拉强度、屈服强度和伸长率分别达到了184.1 MPa、135.5 MPa和8.9%。     

Cu添加对Mg-Bi合金铸态组织和沉淀硬化的影响

制备Mg-5Bi-xCu(x=0,0.2,0.5,1.0，质量分数，%)合金铸锭，研究其铸态组织和沉淀硬化行为。结果表明：铸态Mg-Bi-Cu合金主要由α-Mg枝晶、Mg₃Bi₂相、MgCu₂相和Mg₂Cu相组成，Mg₃Bi₂相和α-Mg基体的取向关系为■,Mg₂Cu相和Mg₃Bi₂相之间的取向关系为■。铸态合金硬度随Cu添加量提高先增大后减小，添加0.5%Cu时硬度最高，为(50.9±1.2)HV。固溶态Mg-5Bi-0.5Cu合金硬度为(49.8±0.9)HV。在175℃时效64 h后，硬度达到峰值(56.1±0.7)HV。时效硬度的提高主要是由于高密度Mg₃Bi₂相的沉淀强化作用，且由于Cu元素的添加，长杆状Mg₃Bi₂沉淀相转变为颗粒状和短棒状Mg₃Bi₂     

热处理对磁场作用下AZ91镁合金焊接接头组织和性能的影响

对5 mm厚的AZ91镁板进行钨极氩弧焊的过程中,外加纵向交流磁场,并在焊后进行固溶、固溶时效和时效处理. 通过对接头显微组织和力学性能分析,研究磁场参数对热处理后AZ91焊接接头组织和性能的影响规律. 结果表明,磁场作用下的AZ91镁合金焊接接头比未施加磁场的焊接接头经固溶处理后晶粒更加细小;经固溶时效处理后更多细小弥散的β-Mg₁₇Al₁₂相大量在α-Mg上析出;经时效处理后析出的β-Mg₁₇Al₁₂相更加细小、断续、分散,且施加磁场的焊接接头比未加磁场的焊接接头热处理后硬度、强度和塑性都得到提高.     

Refinement role of electromagnetic stirring and strontium in AZ91 magnesium alloy

Effect of strontium (Sr) addition and electromagnetic stirring on the microstructure of AZ91 alloy and refinement mechanism were investigated. It was found that Sr addition ranging from 0.1 to 0.3 wt.% caused refinement of as-cast microstructure, but did not form any new phases. Combined strontium alloying and electromagnetic stirring significantly decreased the grain size, changed the morphologies of the β-Mg₁₇Al₁₂ phases and reduced their volume percentage. The smallest grain size of AZ91 alloy was obtained in the case of 0.2 wt.%Sr addition with exciting voltage of 100 V. The increase of Vickers hardness (HV) and Brinell hardness (HB) value of AZ91 alloy were as a result of increasing solid solubility of solute elements (Al, Zn) in the matrix and refining-grain strengthening effect. The microstructural refinement was mainly attributed to the increase of the degree of undercooling and nucleation temperature of primary phase on the basis of DTA analysis results.     

Influences of Ca and Y Addition on the Microstructure and Corrosion Resistance of Vacuum Die-Cast AZ91 Alloy

The influences of Ca and Y additions on the microstructure and corrosion resistance of vacuum die-cast AZ91 alloys were investigated by optical microscope,electron scanning microscope,weight-loss test,and electrochemical corrosion experiment.The results indicate that the Ca or Ca and Y additions refined the microstructure and decreased the amount of Mg17Al12 phase on grain boundaries in the alloys.Meanwhile,the addition of Ca and Y led to the formation of network Al2 Ca phase and rod-like Al2 Y phase,improved the corrosion resistance of AZ91 magnesium alloy.Compared with AZ91 alloy,the corrosion rate of AZ91–1.5Ca–1.0Y alloy was decreased to 16.2%,and its corrosion current density was dropped by one order of magnitude after immersion in 3.5 wt% NaCl solution for 24 h.     

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...     

微量稀土Sm对AZ91D显微组织和腐蚀性能的影响

利用扫描电镜 (SEM) 结合能谱分析 (EDS)、X射线衍射 (XRD)、腐蚀失重实验、电化学极化曲线等方法,研究了0.1%,0.4%,0.7%和1.0%的Sm对AZ91D合金的微观组织和腐蚀性能的影响,并对其腐蚀机理进行分析。结果表明：随着Sm含量的增加,合金中粗大的枝状第二相 (β-Mg₁₇Al₁₂) 逐渐断裂变小,其体积分数下降,因为Sm会结合Al形成颗粒状的Al₂Sm和杆状的Al₃Sm,从而减少晶界处第二相的数量,使第二相呈不连续分布;AZ91D的耐腐蚀性随着Sm加入量的增多,先增加后降低;当Sm加入量为1.0%时,合金的耐腐蚀性与不添加Sm的AZ91D接近;Sm的最佳添加量为0.4%。     

Microstructures and mechanical properties of double hot-extruded AZ80＋xSr wrought alloys

The effects of Sr addition on microstructures and tensile properties of the as-cast and hot-extruded AZ80 alloys were studied by OM, SEM, EDS, XRD, DSC and Instron tester. The results show that the microstructures of as-cast alloys consist of a-Mg and β-Mg17Al12 phase. Sr gathers on the boundaries, and dissolves into β-Mg17Al12 phase or forms Mg17Sr2 phase. The grains of ascast alloys are refined and discontinuous net-shaped structure is formed. The compound phases on the boundaries become thicker with increasing Sr content. The ultimate tensile stress（UTS） and elongation are improved compared with the corresponding Sr-free alloy. After preliminary hot-extruding, the UTS is up to 308-320 MPa and elongation reaches 8.0%-13.5%. After double hot-extrusion, the dynamic recrystallization completes totally, and the UTS is up to 310-355 MPa, but the elongation does not change apparently. The alloy with 0.02%Sr （mass fraction） obtains the best comprehensive performance with the UTS of 355 MPa and elongation of 13.2%. The SEM morphology of fracture surface shows that the alloys with Sr present good ductility after double hot-extrusion.     

Electrochemical behaviour assessment of novel Mg-rich Mg–Al–RE alloys (RE = Ce, Er)

The electrochemical behaviour of new Mg–Al–RE (RE = Ce, Er) alloys AE91 was investigated in 0.01 M NaCl electrolyte (pH = 12) and compared with that of the most commonly used Mg alloy in the automotive field, the AZ91D. Scanning electron microscopy and quantitative electron probe microanalysis were used to characterize the samples prior to the electrochemical tests. AE91 alloys showed very similar microstructures characterized by a three-phase appearance: a Mg-based solid solution containing only Al and two intermetallic phases γ(Mg₁₇Al₁₂) and (Al_1 − xMg_x)₃Ce or (Al_1 − xMg_x)₂Er. Free corrosion potential measurements, potentiodynamic polarization curves and electrochemical impedance spectroscopy revealed improved passivity behaviour compared to AZ91D alloy. The apparent presence of trace amounts of rare earth oxides in the passive film is presumed to be the reason for the enhanced corrosion resistance of AE91 alloys in the aggressive environment considered.