Studies on the influence of process parameters on the AISI 316L resistance spot-welded specimens

Energy saving and improving product performance are long-term concerns in extrusion process. Therefore, this paper proposes a novel extrusion process called alternate extrusion (AE). The proposed process uses split punches alternately instead of the overall structure to apply the downward load, but receives an unexpected load-saving and grain refinement effect. Experimental and finite element method (FEM) methods were used to investigate the effects of different extrusion ratios on microstructure and mechanical properties. Results indicate that load value is significantly reduced, grain size is considerably refined, and tensile strength and elongation of material are improved after AE processing. The fractography shows that the fracture mode of AZ31 magnesium alloy changes from brittle to ductile. Although the actual extrusion ratio decreases in AE process, additional shear forces produced by different punch-alternating loads at the interface improve microstructure and mechanical properties. Therefore, AE can achieve grain refinement and load saving and improve strength and plasticity of magnesium alloys.     

AZ31镁合金静液挤压试验研究

针对镁合金静液挤压工艺所需设备价格昂贵、没有国产设备的问题,研制了能应用在国产低成本普通压力机上的静液挤压试验装置,并解决了耐高压模具、镁丝挤压速度控制、挤压过程温度自动控制及高压热密封等几个关键技术问题。应用最小二乘法进行曲线拟合,得到了不同挤压比条件下温度与单位静液挤压力数量关系的回归方程。应用国产3150kN 液压机进行了静液挤压工艺试验,得到了力学性能优于轧制丝材的AZ31静液挤压镁合金丝。     

Application of ANN to the hot extrusion of magnesium alloy sheets

During the hot extrusion of magnesium alloy, its structure is hexagonal close-packed, which has fewer slide surfaces than aluminium alloy. Experiments show that if the hot extrusion of magnesium alloy sheets is performed under a die that has a high extrusion ratio of 35.9, and a fixed speed is adopted, all of the final products carry defects. Restated, sound sheets with zero-defects cannot be obtained. Further experiments were performed on the extrusion of magnesium alloy sheets by the multi-speed method (MSM), and sound sheets were obtained. However, when the multi-speed method of extruding was used, adjusting the initial speed at the appropriate time directly affected the results of experiments. This paper addresses an experiment designed by the method of orthogonal array (OA), and uses magnesium alloy AZ31 and AZ61 as outer OAs, whereas the factors selected as inner OAs are the temperature of the container, the temperature of the material, the initial speed of extrusion, the final speed and the lubricant. Moreover, the OA of L₁₈ is selected to conduct experiments repeatedly and then apply artificial neural networks (ANN) to learn the results of the experiment. To forecast the temperature of the material for an experiment between 340 and 390 °C, curves of the timing of an adjustment of the initial speed of extrusion by the multi-speed method with increments of 5 °C should be plotted. Experiments are performed to confirm the accuracy of ANN analysis.     

AZ91D镁合金管件挤压成形技术研究

采用在5000kN液压机上进行了AZ91D合金管件的挤压成形工艺生产试验研究，研究了挤压温度、模具预热温度、润滑剂、挤压比等工艺参数在镁合金管件挤压过程中的影响并确定了管件挤压合理的工艺参数。试验得出，挤压成形镁合金管件具有较好的力学性能：抗拉强度吼在289．7～308．9MPa之间，屈服强度σ。在276．106-288．795MPa之间，伸长率占在7．5％～10．1％之间。     

Investigating the characteristics of AZ61 magnesium alloy on the hot and semi-solid compression test

The characteristics of magnesium AZ61 in semi-solid state have been investigated to understand the changes in its stress-strain in the compression process, the effects on its strain under different processing temperatures, and the consequence of the change of peak stress. First, the AZ61 magnesium alloy is heated to 660 °C and sustained at that temperature for 5 min. Then by natural cooling, the cooling curve is acquired. This natural cooling experiment immediately reveals the semi-solid temperature range of AZ61 magnesium alloy. On this temperature range, the study of its semi-solid characteristics and the observation of microstructure can be carried out. After that, the observed results determine the experimental conditions of semi-solid compression. The compression experiment primarily has two parts. One is to understand the changes of AZ61 magnesium alloy from normal temperature to 400 °C, and the other is to carry out the compression experiment of AZ61 magnesium alloy under semi-solid temperature. Upon completion of the experiment, this research explores their microstructures, and compares the structural change of AZ61 magnesium alloy in a hot chamber within the semi-solid temperature range.     

Fabrication of Carbon Nanotubes and Rare Earth Pr Reinforced AZ91 Composites by Powder Metallurgy

It can be known from a large number of research results that improving the dispersibility of CNTs can effectively opti-mize the mechanical properties of the corresponding metal matrix composites.However,the crucial issue of increas-ing the bonding of CNTs and the matrix is still unsolved.In this paper,a novel method was developed to increase interfacial bonding strength by coating titanium oxide(TiO2)on the surface of CNTs.The rare earth Pr and TiO2@CNTs-reinforced AZ91 matrix composites were successfully fabricated by powder metallurgy.Hot press sintering and hot extrusion of the milled powder was performed.After hot extrusion,the influence of TiO2@CNTs on the microstruc-ture and mechanical properties of the composites were investigated.The results showed that the coating process can improve the distribution of CNTs in Mg alloy.The CNTs refined the grains of the matrix,and the CNTs were presented throughout the extrusion direction.When the TiO2@CNTs content was 1.0 wt.％,the yield strength(YS),ultimate ten-sile strength(UTS),and elongation of the alloy attained maximum values.The values were improved by 23.5％,82.1％,and 40.0％,respectively,when compared with the AZ91 alloy.Good interfacial bonding was achieved,which resulted in an effective tensile loading transfer at the interface.CNTs carried the tensile stress and were observed on the tensile fracture.     

Analytic and experimental method for making magnesium alloy products based on an injection moulding process

Magnesium alloys are very attractive materials for the machinery industry, where a lighter weight and a higher strength are needed. Due to the higher ratio of strength versus weight and stiffness versus weight, various magnesium alloys have been tried to make a light and strong product through an extrusion or a die-casting process. However, it was very difficult to achieve these objectives with conventional processes. So, a new process was considered. An injection moulding technology is rising as an alternative solution. In this study, a computer simulation and experiments based upon the injection moulding process were conducted for the AZ91D magnesium alloy. Filling time and melt front temperature were obtained by the simulation. From the injection moulding experimentation, a successful product was made and the product test was conducted.     

Friction stir welding of AZ61A magnesium alloy

This paper deals with the development of an empirical relationship to predict tensile strength of friction stir welded AZ61A magnesium alloy. The process parameters such as tool rotational speed, welding speed, axial force and tool pin profile play a major role in deciding the tensile strength. The response surface method (RSM) was used to develop the empirical relationship. The four-factor, five-level central composite design was used to minimize the number of experimental conditions. The developed empirical relationship can be effectively used to predict tensile strength of friction stir welded AZ61A magnesium alloy joints at 95 % confidence level.     

挤压比对固相再生ZM6镁合金组织和性能的影响

利用固相再生方法在挤压温度为450℃,挤压比分别为11.1:1、25:1和44.4:1的条件下,将ZM6镁合金屑制备成试样,然后进行微观组织观察和力学性能测试。结果表明:ZM6耐热镁合金在挤压过程中发生部分动态再结晶,挤压比越大,动态再结晶程度越大;合金的抗拉强度和延伸率随挤压比的增大而增大,当挤压比从11.1:1提高到44.4:1时,抗拉强度从204MPa提高到248MPa,延伸率从20.7%提高到27.5%。T6态合金的抗拉强度高于挤压态合金的抗拉强度,T6态合金的延伸率低于挤压态合金的延伸率。     

AZ31B镁合金TIG焊焊接接头的疲劳性能

对8 mm厚AZ31B镁合金板及其三种TIG焊焊接接头的静载拉伸性能和疲劳性能进行试验研究。试验结果表明AZ31B镁合金母材的静载抗拉强度为245.50 MPa,TIG焊对接接头、纵向角接接头和非承载十字接头的静载抗拉强度分别为193.55 MPa、229.89 MPa、227.39 MPa。脉动循环(r = 0)疲劳试验表明,在2×106循环次数下,AZ31B镁合金母材的疲劳强度为57.81 MPa,为其静载抗拉强度的23.5％。相同循环次数下,AZ31B镁合金TIG焊对接接头、纵向角接接头和非承载十字接头的疲劳强度为24.60 MPa、20.14 MPa、17.25 MPa,分别为母材疲劳强度的42.6 %、34.8 %和29.8 %。按照国际焊接学会的规范,发现镁合金焊接接头的疲劳级别FAT仅为相应铝合金接头疲劳级别FAT的一半。由此看来,疲劳性能是影响镁合金在承受动态载荷结构中应用的主要因素之一。     

Effect of heat treatment and number of passes on the microstructure and mechanical properties of friction stir processed AZ91C magnesium alloy

In this paper, the effect of heat treatment and number of passes on microstructure and mechanical properties of friction stir processed AZ91C magnesium alloy samples were investigated. From six samples of as-cast AZ91C magnesium alloy, three plates were pre-heated at temperature of 375°C for 3 hours, and then were treated at temperature of 415°C for 18 hours and finally were cooled down in air. Three plates were relinquished without heat treatment. 8 mm thick as-cast AZ91C magnesium alloy plates were friction stir processed at constant traverse speed of 40 mm/min and tool rotation speed of 1250 rpm. After process, microstructural characterization of samples was analyzed using optical microscopy and tensile and Vickers hardness tests were performed. It was found that heat treated samples had finer grains, higher hardness, improved tensile strength and elongation relative to non-heat treated ones. As the number of passes increased, higher UTS and TE were achieved due to finer grains and more dissolution of β phase (Mg₁₇Al₁₂). The micro-hardness characteristics and tensile improvement of the friction stir processed samples depend significantly on grain size, removal of voids and porosities and dissolution of β phase in the stir zone.

     

铸锻复合成形后AZ91镁合金的组织和力学性能

通过铸锻(压铸和模锻)复合成形方式制备了AZ91镁合金汽车转向控制臂,对控制臂主要受力部位的显微组织和力学性能进行了研究,并对拉伸断口进行了分析。结果表明:铸锻复合成形后,AZ91镁合金转向控制臂不同区域的变形量不同,变形量大的区域呈明显的流线特征,并发生动态再结晶,为细小的等轴晶;与压铸态相比,铸锻复合成形后合金的抗拉强度、屈服强度、伸长率及硬度分别为251.3MPa、156.9MPa、4.12%和125HV;断裂机制由脆性断裂变为韧脆混合断裂。     

AZ31镁合金板材在热处理中组织和性能的演变

研究了热处理对AZ31镁合金轧制板材显微组织、室温力学性能和成形性能的影响。热处理温度在300～350℃范围时,显微组织观察表明,热处理后孪晶消失、组织逐渐趋于均匀化、平均晶粒尺寸变小;力学性能和胀形性能测试结果表明,板材的屈服强度明显降低、抗拉强度略有下降、屈强比降低、伸长率提高,杯突值提高。在350℃、15 min空冷处理后,AZ31镁合金板材的综合性能最好。     

AZ31镁合金手机外壳冲压模具的设计与成形工艺

设计了手机外壳冲压模具,研究了镁合金薄板温度、模具温度、拉深速度以及润滑条件对AZ31镁合金手机外壳成形质量的影响。结果表明:镁合金薄板在加热到350～400℃,且凹模的温度不低于薄板温度,较低的凸模温度(50～90℃),较低拉深速度(6mm·s-1)及仅对薄板与凹模和压边圈接触部位润滑的条件下,可以制备出尺寸精度较高的镁合金手机外壳。     

快速凝固结合粉末冶金法制备SiC_p/AZ91复合材料的组织及性能

用快速凝固结合粉末冶金法制备了SiC颗粒增强镁合金基复合材料(SiCp/AZ91)棒材,研究了SiC颗粒含量对复合材料室温力学性能及显微组织的影响.结果表明:制备的复合材料棒材中SiC颗粒在基体中分布均匀,但仍存在局部颗粒团聚现象;随SiC颗粒含量的增加,复合材料的屈服强度、抗拉强度和断后伸长率均逐渐降低;热挤压过程中,镁、SiC和SiO2之间发生了界面反应,在界面生成Mg2Si等脆性相,影响了复合材料的界面性能.     

热处理对含微量镧AZ91镁合金组织和性能的影响

用XRD、SEM、EDS和显微硬度仪等研究了固溶、时效处理对真空精炼的含0.164 8%(质量分数)镧AZ91镁合金显微组织和力学性能的影响。结果表明:加入微量镧后的AZ91镁合金在410℃×24h空冷固溶+170℃×30h空冷时效后,第二类β相大量析出,且呈不连续层片状沿晶界两侧分布;时效态含镧AZ91镁合金的抗拉强度、屈服强度、伸长率和显微硬度分别比铸态不含镧AZ91合金的提高了41.84%,65.08%,35.65%和47.62%;其原因是微量镧改变了热处理中铝原子的扩散状态,有效控制了第一、二类β-Mg17Al12相析出时的形态与分布。     

Microstructure Evolutions during the Hot Extrusion Process of AZ 31B Magnesium Alloy

The hot bulk deformation processes (such as extrusion, forging and rolling) are efficient ways to produce fine microstmcture. The effects of extrusion parameters on the evolved microstructure of directly extruded AZ 31B magnesium alloy were investigated. Extrusion processes were carried out at five different combinations with ram speed ranging from 2 to 8 mm·s-1 and billet temperature ranging from 350 to 450 ℃. The experimental results show that the peak extrusion force decreases with increase in billet temperature and decreases in ram speed. During all the extrusion the profile temperature and die temperature rise continuously. Small particles of secondary phase (β-Mg17A112) are uniformly distributed near the edge of the extruded profiles whereas their distribution is nonuniform in the centre of the extrudates. The size of secondary phase particles present in the central region of the specimens was found to increase with billet temperature and extrusion speed. All the specimens showed mixed microstructure-In the central region of the specimen, low volume fraction of dynamically recrystallized fine grains presented at the grain boundaries of original coarse grains; but near the edge region, the microstructure consisted nearly equiaxed free reerystallized grains.     

挤压态镁合金AZ80动态再结晶机理及性能研究

探讨了挤压态镁合金AZ80的显微组织及动态再结晶机理。利用扫描电镜分析了材料的拉伸性能,并采用T6工艺研究了其热处理性能。结果表明：镁合金AZ80挤压后,出现细小的动态再结晶晶粒,其动态再结晶的机制属于连续动态再结晶;挤压后,材料的强化机制主要是晶粒细化作用。镁合金经过固溶处理后,β-Mg17Al12相已全部溶解到了α-Mg基体中,形成了过饱和的α-Mg固溶体,随着时效温度的升高,β-Mg17Al12相析出机理为从不连续析出到连续析出。     

Mg-12Gd-3Y-0.5Zr镁合金的显微组织、力学性能及时效析出相

通过光学显微镜、扫描电子显微镜、透射电镜、X射线衍射仪、高温拉伸试验机等对不同状态下Mg-12Gd-3Y-0.5Zr镁合金的显微组织、高温力学性能及时效析出相进行了分析。结果表明:该合金铸态组织由α-Mg固溶体、Mg5Gd析出相及α-Mg+Mg24Y5共晶体组成;挤压变形后合金的晶粒尺寸明显减小;合金挤压轧制板材在常温及150℃时有较高的抗拉强度,当温度进一步升高时强度下降较快;合金轧制板材时效析出相在高温(高于250℃)拉伸过程中没有发生相变,但在拉伸过程中会改变分布及形貌,使得变形抗力减小。     

Investigation on overlap joining of AZ61 magnesium alloy: laser welding, adhesive bonding, and laser weld bonding

This paper presents the research on weldability of magnesium alloy AZ61 sheets by overlap laser welding, adhesive bonding, and laser seam weld bonding processes. Microstructures and mechanical properties of the joints are investigated. In overlap laser welding, the joint fractures at the interface between the sheets and maximum shear strength can reach 85% of that of the base metal. Off-center moment during tensile shear test can lead to the strength loss, while the weld edge can also influence the strength as a cracking source. Adhesive bonded joint can offer high tensile shear failure force but low peel strength. Laser weld bonded joint offers higher tensile shear failure force than either laser welded joint or adhesive bonded joint does, and the improved failure load is due to combined contribution of the weld seam and the adhesive. The weld seam can block the adhesive crack propagation, and the adhesive improves the stress distribution, so they can offer a synergistic effect.