压铸态7085铝合金的热变形行为与力学性能研究

以压铸态7085铝合金为研究对象,采用三种工艺对其进行热压缩变形。采用光学显微镜(OM)对热压缩变形试样的微观组织进行观察和分析,采用电子万能试验机和扫描电子显微镜(SEM)对不同工艺下的试样进行力学性能测试和断裂行为分析。结果表明,该合金经不同道次变形后组织差别较大,单道次大应变变形后组织未发生明显的再结晶,为加工硬化状态,而多道次小应变累积的变形方式可激发少量的静态再结晶。单道次等温压缩后材料的屈服强度和抗拉强度较高,分别为402.6和480.7 MPa,断后伸长率从铸态的11.3%降低到9.3%。经固溶处理后材料的组织均匀性有明显改善,单道次等温压缩获得最佳综合力学性能,屈服强度降低到348.0 MPa,断后伸长率增加到20.9%,断口由变形态的沿晶断裂变为穿晶断裂。

压铸态AZ91D镁合金搅拌摩擦焊接头微观组织研究

采用搅拌摩擦焊工艺对4mm厚的压铸态AZ91D镁合金进行对接工艺实验,搅拌头旋转速率1500r/min,焊接速率120mm/min;使用光学显微镜和扫描电镜对焊接接头微观组织进行了研究。结果表明:焊缝外观成形美观,但内部存在贯穿型隧道状孔洞缺陷;焊核区为典型的变形-再结晶组织,为细小、均匀的等轴晶;机械-热影响区为变形-部分再结晶组织,热影响区组织形貌与母材相近但伴有轻微的长大现象;焊核区与机械-热影响区的过渡具有以下特征:在前进侧呈现"突变"特征,在后退侧呈现"渐变"特征。

基于搅拌摩擦焊驱动模式分析压铸态AZ91D镁合金接头隧道状缺陷形成原因

采用不同焊接规范对压铸态AZ91D镁合金进行搅拌摩擦焊连接,并采用光学显微镜、扫描电镜等方式对焊缝接头微观形貌进行研究。结果表明,焊接速率高于60mm/min时,焊缝中均产生贯穿型隧道状缺陷,缺陷位于焊缝前进侧冠状区与环形区交界处;随着焊接速率的增大,缺陷有逐渐向焊缝底部延伸的趋势。分析认为该缺陷的形成机理如下:冠状区塑性材料同时受到搅拌针和轴肩共同作用,环形区塑性材料主要受到搅拌针作用,致使环形区与冠状区结合处呈现出流动差异性,导致在前进侧产生隧道状缺陷。

压铸态SiCw/Al复合材料中的热残余应力

利用X射线衍射方法 ,研究了压铸态SiCw/ 60 61Al复合材料中热残余应力。结果表明 ,压铸态复合材料基体中存在三向不等的热残余拉应力 ,各向应力分量差异主要与晶须的择尤取向有关。晶须体积分数越高 ,则晶须的择尤取向程度越明显 。

压铸态AZ91D镁合金热压缩变形流变应力研究

在应变速率为0.01～10 s-1、变形温度250～450℃的条件下,采用Geeble-1500D热模拟机对压铸态AZ91D镁合金进行热压缩变形试验,得到并分析了该材料在不同变形条件下的流变曲线。采用数理统计的方法对实验数据进行处理,建立了用Zener-Hollomom参数描述的该材料的高温塑性变形本构方程为=1.41×1012[sinh(0.014σ)]5.295exp(–159 449.509/RT),采用双曲正弦函数确定了该材料的变形激活能Q=159.45 kJ·mol-1;与重力铸造态AZ91D镁合金比较显示,其流变应力和变形激活能更低。

压铸AZ91D镁合金激光重熔区氢气孔的形成机制

为研究压铸镁合金熔化焊接气孔的形成机理,对厚度为6mm的AZ91D压铸镁合金和厚度为2.2mm的AZ71热挤压镁合金进行CO2激光局部重熔。采用扫描电子显微镜(SEM)观察气孔形貌,利用粒径分析软件Nano measure 1.2测量气孔的尺寸。结果表明:压铸镁合金重熔区气孔问题突出,少数粗大的宏观气孔形状不规则,内壁粗糙,具有明显的金属冲刷痕迹,均来源于母材预存微观气缩孔;多数微观气孔内壁光滑、呈倒喇叭形,属于氢致气孔。分析了氢致气孔的形成机制,建立了氢气孔形成过程的模型,并同实验照片进行了比较,发现所建立的模型能够很好地用来解释氢致气孔的形成过程。

压铸镁合金AZ91D搅拌摩擦焊接头焊核演变机理研究

搅拌针旋转频率为1200r/min、焊接速率为40mm/min条件下,对4mm厚的压铸镁合金AZ91D进行连接,可获得无缺陷的焊缝接头。使用OM,SEM对焊缝接头微观组织进行观察。结果表明:压铸镁合金AZ91D搅拌摩擦焊接头焊核区域微观组织呈现出较大差异,顶部冠状区组织为均匀粗大、高致密度的再结晶晶粒,平均晶粒约为15μm;中心环形区域及焊核底部组织相对细小,均匀程度不如焊核冠状区;焊核区组织均为再结晶晶粒,晶粒形核模式与非连续动态再结晶模式类似。

压铸SiC_W/6061Al复合材料中晶须取向分布与热残余应力

应用扫描电镜一图像仪联机系统，定量测量压铸态SiCW／6061Al材料中晶须取向分布。借助X射线应力仪，测定复合材料中的残余应力。结果表明，晶须在垂直压铸方向有择优性，残余应力在垂直压铸方向的分量较大。随温度升高，残余应力的变化为：拉应力→零应力→压应力，各应力分量具有相近的零应力温度。低温处理可降低材料室温残余应力及零残余应为温度。

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Al_(11)Nd_(3),原有的半连续网状分布的β-Mg_(17)Al_(12)数量有所减少。压铸态AZ91D-1.11Nd合金呈现良好的综合性能,室温抗拉强度、伸长率和热导率分别为272 MPa、12.0%和69.5 W/(m·K),与AZ91D合金相比分别提高14%、100%和14%;同时呈现与AZ91D合金相当的优异铸造工艺性能,流动长度达到1161 mm。

Mg-6.4La-4.87Al镁合金的金属型和压铸组织与性能

制备铸态与压铸态Mg-6.48La4.87Ar两种合金试样,采用OM、SEM和XRD分析其微观组织和相组成,并测试室温拉伸与压缩力学性能、导热性能和流动性能。结果表明:铸态晶粒粗大,第二相分布不均匀;经传统压铸后,晶粒变得细小,第二相分布均匀。两者试样微观组织均主要由a-Mg基体、点状Al_(11)La_(3)相和少量针状Mg_(12)La相组成。铸态试样抗拉强度、抗压强度和伸长率分别为157MPa、263MPa和4.0%,经压铸后试样抗拉强度、抗压强度和伸长率分别提高至236MPa、345MPa和4.5%,较铸态值分别提高63%、31%和13%,同时呈现较好的流动性能,流动长度为1374mm。铸态试样导热系数达到113.2W/(m·K),经压铸后仍能保持较高的导热系数,为90.9W/(m·K)。

凝固条件对Al-Si复合材料中共晶Si形貌的影响

为了优化压铸态Al2O3f/Al-15Si复合材料中Si相组织,利用金相和SEM分析了Al-15Si合金和Al2O3f/Al-15Si复合材料中Si相在不同冷却方式下的形貌特征.结果表明:压铸态和重熔后炉冷态的Al-15Si合金中共晶Si均为片状,而Al2O3f/Al-15Si复合材料内共晶Si由片状转变为棒状;Al2O3f/Al-15Si复合材料750℃重熔后在水淬、模具中冷却和炉冷冷却条件下分别获得了细小变质态、针状及棒状等形态的Si相;炉冷处理可作为优化压铸态复合材料组织的一种途径.

Microstructures and mechanical properties of semi-solid squeeze casting ZL104 connecting rod

Semi-solid squeeze casting（SSSC） and liquid squeeze casting（LSC） processes were used to fabricate a ZL104 connecting rod, and the influences of the process parameters on the microstructures and mechanical properties were investigated. Results showed that the tensile strength and elongation of the SSSC-fabricated rod were improved by 22% and 17%, respectively, compared with those of the LSC-fabricated rod. For SSSC, the average particle size（APS） and the shape factor（SF） increased with the increase of re-melting temperature（Tr）, whereas the tensile strength and elongation increased first and then decreased. The APS increased with increasing the mold temperature（Tm）, whereas the SF increased initially and then decreased, which caused the tensile strength and elongation to increase initially and then decrease. The APS decreased and the SF increased as squeezing pressure（ps） increased, and the mechanical properties were enhanced. Moreover, the optimal Tr, ps and Tm are 848 K, 100 MPa and 523 K, respectively.

Optimization of AZ80 magnesium alloy squeeze cast process parameters using morphological matrix

The squeeze cast process parameters of AZ80 magnesium alloy were optimized by morphological matrix. Experiments were conducted by varying squeeze pressure, die pre-heat temperature and pressure duration using L9（33） orthogonal array of Taguchi method. In Taguchi method, a 3-level orthogonal array was used to determine the signal/noise ratio. Analysis of variance was used to determine the most significant process parameters affecting the mechanical properties. Mechanical properties such as ultimate tensile strength, elongation and hardness of the components were ascertained using multi variable linear regression analysis. Optimal squeeze cast process parameters were obtained.

Microstructural characteristics of Al-20Si-2Cu-0.4Mg-1Ni alloy formed by rheo-squeeze casting after ultrasonic vibration treatment

A swash plate for air conditioning compressor of cars was formed by rheo-squeeze casting with semi-solid Al-Si alloy slurry prepared by ultrasonic vibration process, and the microstructure of this alloy was investigated. Besides the microstructures of primary Si particles and α(Al)+β-Si eutectic phases, non-equilibrium α(Al) particles or dendrites are discovered in the microstructure of the Al-20Si-2Cu-0.4Mg-1Ni alloy. Rapid cooling generated by squeeze casting process rather than the pressure is considered as the main reason for the formation of non-equilibrium α(Al) phase. The sound pressurizing effect of ultrasonic vibration also enables the non-equilibrium α(Al) phases to form above eutectic temperature and grow into non-dendritic spheroids in the process of semi-solid slurry preparation. Non-equilibrium α(Al) phases formed in the hypereutectic Al-Si alloy with ultrasonic vibration treatment, consist of round α(Al) grains formed above the eutectic temperature and a small amount of fine α(Al) dendrites formed under the eutectic temperature. The volume fraction of primary Si particles is decreased significantly by the effect of ultrasonic vibration through increasing the solid solubility of Si atoms in α(Al) matrix and decreasing the forming temperature range of primary Si particles. The average particle diameter and the volume fraction of primary Si particles in microstructure of the swash-plate by rheo-squeeze casting are 24.3 μm and 11.1%, respectively.

Microstructure and mechanical properties of Al-6Zn-2.5Mg-1.8Cu alloy prepared by squeeze casting and solid hot extrusion

Al-6Zn-2.5Mg-1.8Cu alloy ingots were prepared by squeeze casting under different specific pressures,and the fresh ingot with best mechanical properties was solid hot extruded.With the increase of the specific pressure from 0 to 250 MPa,the dendrites became round and small.Because the applied pressure increased the solid solubility of alloying elements,the number of MgZn2 phases decreased.When the specific pressure increased from 250 MPa to 350 MPa,the grain size increased.After solid hot extrusion,the a（Al） grains were refined obviously and the MgZn2 phases were uniformly dispersed in the microstructure.After solid hot extrusion,the ultimate tensile strength was 605.67 MPa and the elongation was 8.1%,which were improved about 32.22%and15.71%,respectively,compared with those of the metal mold casting alloy.The fracture modes of the billet prepared by the metal mold casting and by squeeze casting were intergranular and quasi-cleavage fractures,respectively,whereas,that of the solid hot extrusion was mainly dimple fracture.The refined crystalline strengthening was the main reason to improve the strength and elongation of alloy.

Feasibility of semi-solid die casting of ADC12 aluminum alloy

The feasibility of semi-solid die casting of ADC12 aluminum alloy was studied. The effects of plunger speed, gate thickness, and solid fraction of the slurry on the defects were determined. The defects investigated are gas and shrinkage porosity. In the experiments, semi-solid slurry was prepared by the gas-induced semi-solid （GISS） technique. Then, the slurry was transferred to the shot sleeve and injected into the die. The die and shot sleeve temperatures were kept at 180 ℃ and 250 ℃, respectively. The results show that the samples produced by the GISS die casting give little porosity, no blister and uniform microstructure. From all the results, it can be concluded that the GISS process is feasible to apply in the ADC12 aluminum die casting process. In addition, the GISS process can give improved properties such as decreased porosity and increased microstructure uniformity.

Microstructural characteristics of near-liquidus cast AZ91D alloy during semi-solid die casting

Near-liquidus cast ingot was reheated to semi-solid firstly, and then a bracket of motor was prepared by die casting the semi-solid ingot into mould. The microstructural characteristics of AZ91D alloy in these processes were investigated. In the process of near-liquidus casting, primary α-Mg grains tend to be rosette-like because of the increase of plentiful quasi-solid atom clusters in molten alloy with the decrease of pouring temperature. These rosette-like a-Mg grains in ingots fabricated by near-liquidus casting are fused off and refined into near-globular structure owing to the solute diffusion mechanism and the minimum surface energy mechanism during reheating. After semi-solid die-casting, a-Mg grains, located in biscuit, impact and connect with each other; α-Mg grains, located in inner gate, congregate together; while α-Mg grains, located in component, distribute uniformly and become into globularity or strip. Because the inner gate limits the flowing of semi-solid slurry, and the pressure acted on the semi-solid slurry decreases gradually along the filling direction of semi-solid slurry in Cavity, microstructural segregation of unmelted a-Mg grains appears along this direction. Shrinkage holes in casting are caused by two different reasons. For biscuit, the shrinkage holes are caused by the blocked access of feeding liquid to the shrinkage zone for the agglomerated unmelted α-Mg grains. For component, the shrinkage holes are caused by the lack of feeding of liquid alloy.

Rheo-squeeze casting of semi-solid A356 aluminum alloy slurry

The effect of pouring temperature, electromagnetic stirring power and holding process on semi-solid A356 aluminum alloy slurry was investigated, then the slurry was squeeze-cast. The results show that when the pouring temperatures are properly above the liquidus line, for example 630-650 ℃, the slurry with spherical primary α（Al） grains can be prepared under the stirring power of 1.27 kW. The slurry is then homogeneously held for a short time, and the primary α（Al） grains are further ripened and distributed evenly in the slurry. The results of the rheo-squeezed casting experiments show that the injection specific pressure has a great effect on the filling ability of the semi-solid A356 aluminum alloy slurry, and the higher the injection specific pressure is, the better the ability for the slurry to fill the mould cavity is. When the injection specific pressure is equal to or above 34 MPa, the whole and compact rheo-squeezed castings can be obtained. The microstructure of the castings indicates that the shape, size and numbers of the primary α（Al） grains in different parts of the castings are highly consistent. After being held at 535 ℃ for 5 h and then aged at 155 ℃ for 12 h, the ultimate strength of the rheo-squeezed castings can reach 300-320 MPa, the yield strength 230-255 MPa, and the elongation 11%-15%.

Effect of twinning on flow stress during initial stage of hot compression of twin roll cast Mg-5.51Zn-0.49Zr alloy

A Thermecmastor-Z hot deformation simulator,optical microscopy,XRD and TEM were employed to characterize the flow stress behavior and microstructure of twin roll cast ZK60 magnesium alloy during initial stage of hot compression at elevated temperature of 300 ℃ and 400 ℃ and a given strain rate of 10-2s-1.The results suggest that flow stress drop during initial stage of hot compression at 300℃,generally led by dynamic recrystallization,is attributed to twinning,correspondingly to dynamic recrystallization as deformation temperature is raised to 400 ℃.

Processing map and hot deformation behavior of squeeze cast 6082 aluminum alloy

The hot deformation behavior and microstructure evolution of 6082 aluminum alloy fabricated through squeeze casting(SC)under different pressures were studied.The alloy was subjected to hot compression tests and 3D hot processing maps were established.The microstructure evolution was studied by optical microscope(OM),scanning electron microscope(SEM),and electron backscattered diffraction(EBSD).It is found that more dynamic recrystallization(DRX)grains are generated during the deformation of the specimen fabricated under higher SC pressure.At high temperature the effect of SC pressure on microstructure evolution weakens due to the dissolution of second phase particles.In addition,uneven second phase particles in specimens fabricated under higher SC pressure compressed with low temperature and middle strain rate would result in flow localization instability.Finally,the optimum deformation conditions for the 6082 aluminum alloy fabricated by SC were obtained at the temperatures of 430−500℃ and the strain rates of 0.01−1 s^(−1).