搅拌摩擦加工制备羟基磷灰石增强镁复合材料的微观组织和力学性能

通过搅拌摩擦加工（Friction stir processing,FSP）制备了羟基磷灰石增强镁（HA/WE43）复合材料,研究了主轴转速对HA分布的影响及FSP加工前后材料微观组织和力学性能的变化。使用光学显微镜、SEM、TEM对该复合材料的显微组织进行了表征,同时对其显微硬度和室温拉伸性能进行了测试。结果表明:制得的HA/WE43复合材料晶粒尺寸相比于母材发生了显著的细化,加工过程中,HA颗粒的存在增强了FSP的晶粒细化作用;主轴转速较低时,HA/WE43复合材料中的HA团聚较严重,随着主轴转速的增加,HA的分布更加均匀,团聚现象得到改善;尽管局部团聚的HA颗粒会成为复合材料在拉伸变形过程中的裂纹源,但HA/WE43复合材料的极限抗拉强度、屈服强度和伸长率相对于母材仍有明显提高。      

水下多道次搅拌摩擦加工对纯铜微观组织和力学性能的影响

目的 分别在空气中和水中对铜板进行单道次和多道次搅拌摩擦加工（FSP）,以此探究冷却介质和加工道次对纯铜微观组织和力学性能的影响。方法 选择厚度为3 mm的T2纯铜板分别在空气中进行1～2道次加工,在水下进行1～4道次加工。使用光学显微镜、显微硬度检测、扫描电子显微镜和拉伸试验机对加工后的试样进行微观组织和力学性能检测。结果 与空气中的搅拌摩擦加工相比,水下搅拌摩擦加工试样的表面质量更好;空气中搅拌摩擦加工试样的晶粒尺寸比母材的晶粒尺寸大,水下搅拌摩擦加工（SFSP）可以有效细化晶粒,并且随着加工道次的增加,晶粒尺寸逐渐增大,其中,1道次水下搅拌摩擦加工纯铜的晶粒尺寸最小（3.93μm）。显微硬度检测和拉伸试验结果表明,与空气中搅拌摩擦加工试样相比,水下搅拌摩擦加工试样的屈服强度和硬度更高,但随着加工道次的增加,样品的屈服强度和硬度都会有所降低。结论 水下多道次搅拌摩擦加工可以减小纯铜的晶粒尺寸,提升纯铜的力学性能。     

搅拌摩擦加工对Al2O3/B4C/Al复合材料室温及高温力学性能的影响

目的研究搅拌摩擦加工对Al_2O_3/B_4C/Al复合材料力学性能的影响。方法将球形铝粉球磨成片状后氧化,并向其中混入质量分数为10%的碳化硼颗粒,热压成形后锻压,对锻饼进行一道次的搅拌摩擦加工,研究搅拌摩擦加工后复合材料的室温与高温力学性能。结果通过搅拌摩擦加工能显著提高材料室温强度,但与锻压态材料相比,材料高温强度降低。结论晶界处氧化铝对材料高温性能有重要影响,搅拌摩擦加工使晶界处氧化铝破碎并进入晶粒内部,提高了室温强度,但不利于提高高温性能。     

搅拌摩擦加工对原位TiB2/7075复合材料性能的影响

用搅拌摩擦加工法处理原位自生TiB2/7075复合材料,分析了经过不同加工道次的复合材料的微观结构、拉伸性能。结果表明:经过搅拌摩擦加工,搅拌区内的复合材料晶粒细小,颗粒大团聚被打散,颗粒在微米尺度分布更为均匀,同时消除了在制备过程中产生的浇铸缺陷。在搅拌区内复合材料的晶粒直径由45μm细化到2μm。与一道次加工相比,经过四道次搅拌摩擦加工的复合材料,其微观组织形貌更为均匀。缺陷的消除以及微观组织的改变,使复合材料搅拌区的拉伸性能得到显著提高,四道次加工的材料断裂强度为母材的1.3倍,而延伸率则为母材的8倍。     

铝合金搅拌摩擦焊接头微观组织和力学性能分析

目的 研究7020铝合金搅拌摩擦焊(FSW)的结构和机械性能。方法 采用搅拌摩擦焊对铝板进行对接焊试验,具体形式为单面焊双面成型。采用拉伸机和显微维氏硬度仪对试样进行力学性能测试;利用蔡司金相、光谱仪、扫描电子显微镜、X射线衍射仪研究母材和焊接接头的微观组织。结果 在硬度上,母材>热影响区>焊核区,热影响区平均硬度约为94HV,母材平均硬度为99HV,焊核区平均硬度最低为78HV,焊核区出现“S”缺陷,在一定程度上弱化了焊核区性能;7020铝合金搅拌摩擦焊接头的抗拉强度为235 MPa,屈服强度为158 MPa,屈强比为0.67,伸长率为7%,焊接系数可以达到73.8%;母材的抗拉强度为325 MPa,屈服强度为278 MPa,屈强比为0.86,伸长率为25%;焊接接头中心显微组织主要由胞状树枝晶体组成,显微结晶依次呈现为平面晶、胞状晶、树枝状晶、等轴晶;铝合金母材和焊接接头的金属相组成均为α?Al+Mg2Si;焊接接头断口呈现比较明显的韧性断裂特征。结论 铝合金搅拌摩擦焊可以获得性能比较优良的焊接接头,为其他铝合金材料的FSW焊接提供技术参考。     

搅拌摩擦加工铝基复合材料的高温摩擦磨损性能

通过在铝合金表面一定深度添加颗粒度为10μm的B4C粉末,采用搅拌摩擦加工方法制备成铝基复合材料.采用SEM、EDS、高温摩擦磨损试验机对其摩擦磨损性能进行研究;分析加工方法和环境温度对摩擦因数和磨痕形貌的影响,并探讨磨损机制.结果表明:高温磨损条件下,搅拌摩擦加工制备的铝基复合材料能明显改善铸态ZL109铝合金的耐磨性;复合材料表现出较好的磨损性能和较低的摩擦磨损因数.搅拌摩擦加工制备的铝基复合材料在100℃时磨损以氧化磨损和磨粒磨损为主,随着温度的升高,300℃时复合材料的磨损机理由氧化磨损转变为黏着磨损.     

搅拌针形状对搅拌摩擦加工制备CNTs/铝基复合材料均匀性的影响

采用搅拌摩擦加工技术(FSP)制备碳纳米管增强铝基(CNTs/Al)复合材料,研究了搅拌针形状对复合材料均匀性的影响。结果表明:搅拌针形状影响到塑化材料的迁移路径和程度,导致复合材料宏观形貌和均匀性发生变化。相比柱形,锥形搅拌针周围金属温度高,挤压区易于扩张,抽吸-挤压效应较强,形成的中心区面积大且均匀性较好;双螺纹搅拌针由于在板材上下两端形成两个材料迁移通道,挤压区相互重叠,材料混合程度加强,中心区CNTs分布均匀性最好。     

5083铝合金搅拌摩擦焊接头的显微组织与力学性能

对8 mm厚5083-H321铝合金板进行了搅拌摩擦焊接试验,研究了焊接工艺参数对搅拌摩擦焊接头显微组织和力学性能的影响。结果表明:该搅拌摩擦焊接头焊核区显微组织为细小的等轴晶组织,热机影响区为拉伸弯曲变形组织,热影响区非常窄,其晶粒尺寸与母材相当;综合接头表面形貌和拉伸性能得到较佳的搅拌摩擦焊接工艺参数为使用搅拌针为三棱形带螺纹、轴肩为内扣型的搅拌头,主轴转速为300 r·min^-1,焊接速率为120 mm·min^-1;在该工艺条件下接头表面成形良好,抗拉强度可达到母材的94.5%。     

转速对6061铝合金搅拌摩擦搭接焊接头组织和力学性能的影响

目的 研究不同转速条件下6061铝合金搅拌摩擦搭接焊接头组织和力学性能的变化规律,为工程实践应用提供参考。方法 在不同旋转速度（800、1 200、1 500 r/min）下对4 mm厚的6061铝合金进行搅拌摩擦搭接焊实验,固定进给速度和轴肩下压量,研究搅拌头转速对接头宏观组织、微观组织和力学性能的影响。结果 所有接头均没有出现明显缺陷,当转速为1 500 r/min时,搅拌区晶粒尺寸细化明显,最大失效载荷达到母材的75%,上板和下板的硬度曲线都呈“W”形;当转速为800 r/min和1 200 r/min时,下板硬度曲线呈“V”形。随着转速的增大,有效搭接宽度逐渐增大,接头的平均拉剪强度也在增大,所有接头都在前进侧断裂,断裂形式均为拉伸断裂。结论 转速的提升增加了焊接热输入量和机械搅拌作用,促进了有效搭接宽度的增大和晶粒尺寸的细化,但未能改变钩状缺陷的形成及延伸方向。当转速为1500r/min时,热输入量较大,搅拌区范围相对较大,下板存在更大面积的搅拌区,其硬度规律与上板的相似。所有接头均为拉伸断裂,断裂位置在热影响区附近,说明搭接接头连接良好。     

A356Al/TiB2颗粒增强铝基复合材料的搅拌摩擦焊

采用纯机械化的固相连接技术--搅拌摩擦焊成功地焊接了应用原位反应合成法制造的铸态A356Al/6.5%TiB2(体积分数)颗粒增强铝基复合材料,与铝合金相比,铝基复合材料搅拌摩擦焊的焊缝质量对焊接参数更为敏感.该连接方法在较低温度下实现铝基复合材料的焊接,避免了基体铝合金与增强相之间的化学反应,同时在搅拌头机械搅拌、挤压和摩擦热的共同作用下,焊缝区基体材料的晶粒和增强相被破碎并形成再结晶晶核,细化了组织结构,增强相分布也更加弥散.焊缝区的硬度值波动范围很小,抗拉强度比母材增加约20%.研究表明,搅拌摩擦焊用于连接颗粒增强铝基复合材料具有明显的优势.     

搅拌摩擦加工对Al-Si-Fe合金组织和性能的影响

为改善再生铝中富铁相形态,提高其合金性能,本文采用搅拌摩擦加工对Al-Si-Fe合金进行了研究。利用金相显微镜、扫描电镜、万能拉伸试验机、显微硬度计及图形分析仪等研究了加工速度对Al-Si-Fe合金组织和性能的影响。研究结果表明:搅拌摩擦加工后,第二相形态由针状、棒状向细小且均匀分布的球状、粒状和短棒状转变,前进侧热机械影响区组织得到一定程度的细化且具有明显的取向,而返回侧热机械影响区的组织则保持铸态形貌特征的组成。加工中心区的富铁相和共晶硅平均长度较基材分别降低了86.5%、37.4%,而圆整度则分别提高了7.8倍和2.1倍以上,富铁相细化效果优于共晶硅;随着加工速度的提高,富铁相的平均长度逐渐增大,而圆整度则逐渐降低;但加工速度对共晶硅的平均长度影响较小,但圆整度逐渐降低。加工区的抗拉强度、屈服强度大幅降低,最高降幅达55.4%,而伸长率最大可提高6.8倍。随着加工速度的提高,其抗拉强度、屈服强度有所提高,伸长率则逐渐降低,最大降幅达到19.3%。搅拌摩擦加工后,Al-Si-Fe合金晶粒细化,材料性能提升。     

Effect of welding parameters on microstructure and mechanical properties of friction stir spot welded 5052 aluminum alloy

Friction stir spot welding (FSSW) is a newly-developed solid state joining technology. In this study, two types of FSSW, normal FSSW and walking FSSW, are applied to join the 5052-H112 aluminum alloy sheets with 1 mm thickness and then the effect of the rotational speed and dwell time on microstructure and mechanical properties is discussed. The lower sheet material underneath the hook didn’t flow into the upper sheet due to the concave surface in the shoulder and groove in the anvil. The hardness profile of the welds exhibited a W-shaped appearance and the minimum hardness was measured in the HAZ. The results of tensile/shear tests and cross-tension tests indicate that the joint strength decreases with increasing rotational speed, while it’s not affected significantly by dwell time. At the rotational speed of 1541 rpm, the tensile/shear strength and cross-tension strength reached the maximum of 2847.7 N and 902.1 N corresponding to the dwell time of 5 s and 15 s. Two different fracture modes were observed under both tensile/shear and cross-tension loadings: shear fracture and tensile/shear mixed fracture under tensile/shear loadings, and nugget debonding and pull-out under cross-tension loadings. The performance of the welds plays a predominant role in determining the type of fracture modes. In addition, the adoption of walking FSSW brings unremarkable improvements in weld strength.     

Evaluation of the microstructure and mechanical properties of friction stir welded 6005 aluminum alloy

Abstract

The microstructural change related with the hardness profile has been evaluated for friction stir welded, age hardenable 6005 Al alloy. Frictional heat and plastic flow during friction stir welding created fine and equiaxed grains in the stir zone (SZ), and elongated and recovered grains in the thermomechanically affected zone (TMAZ). The heat affected zone (HAZ), identified only by the hardness result because there is no difference in grain structure compared to the base metal, was formed beside the weld zone. A softened region was formed near the weld zone during the friction stir welding process. The softened region was characterised by the dissolution and coarsening of the strengthening precipitate during friction stir welding. Sound joints in 6005 Al alloys were successfully formed under a wide range of friction stir welding conditions. The maximum tensile strength, obtained at 507 mm min^-1 welding speed and 1600 rev min^-1 tool rotation speed, was 220 MPa, which was 85% of the strength of the base metal.     

Effect of friction stir welding on the microstructure and mechanical properties of AA 6063-T6 aluminum alloy

In this study, AA 6063-T6 alloy plates were joined via friction stir welding using three different pin geometries (i. e., helical threaded, pentagonal and triangular) under various process parameters of tool rotational speed and welding speed. The microstructures and mechanical properties of the various welded joints were investigated. Macro-structural observations revealed that kissing bonds occurred in the welded joints due to fractured oxide layers. X-ray diffraction analysis indicated that the stir zones of the welded joints exhibited phases of Al₈Fe₂Si, Al₅FeSi, and Mg₂Si. In the welded joints, processed using a helical threaded pin, no tunnel-type defect was detected to occur; specimens were fractured outside of the joint region during tensile tests, indicating that the kissing bonds formed in the stir zones did not cause any deterioration in tensile strength or ductility. The welded joints processed using a helical threaded, pentagonal and triangular pin at 500 min⁻¹ tool rotational speed and 80 mm min⁻¹ welding speed exhibited a ductile deformation behavior along with a tensile strength in the range of 153 MPa to 155 MPa.     

Effect of welding parameters on microstructure and mechanical properties of friction stir welded joints of AA7039 aluminum alloy

A high strength Al–Zn–Mg alloy AA7039 was friction stir welded by varying welding and rotary speed of the tool in order to investigate the effect of varying welding parameters on microstructure and mechanical properties. The friction stir welding (FSW) process parameters have great influence on heat input per unit length of weld, hence on temperature profile which in turn governs the microstructure and mechanical properties of welded joints. There exits an optimum combination of welding and rotary speed to produce a sound and defect free joint with microstructure that yields maximum mechanical properties. The mechanical properties increase with decreasing welding speed/ increasing rotary speed i.e. with increasing heat input per unit length of welded joint. The high heat input joints fractured from heat affected zone (HAZ) adjacent to thermo-mechanically affected zone (TMAZ) on advancing side while low heat input joints fractured from weld nugget along zigzag line on advancing side.     

Effect of tool pin eccentricity on microstructure and mechanical properties in friction stir welded 7075 aluminum alloy thick plate

Four different tools with the pin eccentricity of 0.1 mm, 0.2 mm, 0.3 mm and 0.4 mm were designed to friction stir weld 10 mm thick AA7075-O plate. The effect of pin eccentricity on microstructure, secondary phase particles transformation and mechanical properties of the joints was investigated. The results show that the nugget area (A_NZ) increases firstly and then decreases with increasing the pin eccentricity. When the pin with 0.2 mm eccentricity is applied, the A_NZ is the largest; meanwhile the grains size is the smallest which is about 3 μm and secondary phase particles are the most dispersive in nugget zone compared with other tools. While the grains are coarsened to 7–11 μm as the eccentricity is more than 0.4 mm, some coarse hardening particles get to cluster in the thermo-mechanically affected zone. The joints produced by the pin with 0.2 mm eccentricity perform the highest tensile strength and elongation, which is attributed to better interfaces, finer grains and more dispersive secondary phase particles.     

Effect of graphite exfoliation through multipass friction stir processing on microstructure and mechanical properties of aluminium 7075-silicon carbide-graphite composites

In this study, friction stir processing techniques has been utilized to fabricate graphite-reinforced aluminium matrix composite. Silicon carbide will be mixed together with graphite flakes as reinforcement with the composition of hybrid ratio 60 : 40. The manipulated variable of this project is the number of passes used during friction stir processing (1, 2 and 3 passes). Three different number of passes are used to investigate its effect onto the reinforcement dispersion inside the aluminium metal matrix composites. Microstructural analysis has shown that with increasing number of passes, the distribution of reinforcement particles becomes more uniform and homogeneous. Nanoreinforcement particle dispersions are observed and analysed. Result shows that the size of agglomerations across the composite surface decreases as the number of passes increases. Further observation and analysis of on the particles has confirmed that graphite flakes have been successfully shear exfoliated into layers to cover more surface area. The overall mechanical properties have also observed significant increase with increasing number of passes. Sample with highest number of pass (3 pass run) managed to achieve maximum tensile strength and elongation percentage of 304.04 MPa and 2.54 %, respectively, which is the highest value among all the samples tested.     

Evolution of microstructure and mechanical characteristics of friction stir welded ultrafine-grained aluminum alloy 6082

Bulk production of ultrafine-grained material is in great demand presently. Ultrafine-grained material can be synthesized using accumulative roll bonding, which is a prominent severe plastic deformation technique to develop such materials in bulk. There are further challenges in the fabrication of ultrafine-grained material. Friction stir welding is a potential technique to join the ultrafine-grained material while maintaining its mechanical and microstructural characteristics stability as no fusion is required. The present research work demonstrates the microstructural and mechanical characteristics of various welding zone after friction stir welding of ultrafine-grained aluminum alloy 6082. The microstructural features were examined using optical microscopy and the electron back-scattered diffraction technique. The variation in mechanical characteristics was observed using tensile and microhardness tests. The fractography of tensile specimens was studied to identify the mode of failure. The present study demonstrates the viability of friction stir welding to join ultrafine-grained aluminum alloy 6082 developed by accumulative roll bonding. The ultrafine grain size of 0.52 μm was achieved after four accumulative roll bonding cycles. The microhardness of accumulative roll bonding processed samples and the tensile strength of the weld joint were increased about two times and 1.6 times respectively compared to the annealed sample.     

Effects of an overlapping multi-pass friction stir process and rapid cooling on the mechanical properties and microstructure of AZ31 magnesium alloy

Applications for magnesium as the lightest structural metal are increasing; however, its low ductility at room temperature could be considered a limitation. The friction stir process (FSP) is a solid state process that can overcome this limitation by producing a fine-grained material and uniform texture. This study used overlapping passes FSP to create a fine-grained area on the surface of AZ31 magnesium alloy. Rapid cooling was employed during the process to eliminate the thermal effects of successive passes. Two different modes of overlap were created. In the first mode, the surface of the sample was FSPed overlapping in one direction. In the second mode, the first overlapped surface of the sample was overlapped again in a direction perpendicular to the primary process. The results showed that mechanical strength in the process direction increased for both modes. Elongation was greater for the first mode than that of the raw material and, for the second mode, was less than for the raw material. In the direction perpendicular to the process, both the mechanical strength and ductility of the material were less than those of the raw material. The particle distribution in the second mode was more uniform than that for the first mode.