Friction stir lap welded advanced high strength steels: Microstructure and mechanical properties

Friction stir welding was carried out under different heat input and cooling rates to produce lap joints between high strength martensitic steel sheets. The microstructure of the welds was characterized, and microhardness was evaluated. Joint efficiency was determined by lap shear test. Variation in processing conditions governed total heat input, peak temperature and cooling rate during friction stir welding. Weld nugget microstructure depended principally on cooling rate. The slowest cooling rate promoted ferrite-pearlite and the fastest cooling rate resulted in martensite formation in the weld nugget. The weakest region of all the joints was the heat affected zone, which consists of ferrite with small quantities of pearlite. Fracture during shear testing occurred along the heat affected zone of welded joints. The width and grain size of ferrite in heat affected zone controlled the joint efficiency.     

超细晶Q460高强钢焊接接头组织与韧性研究

采用手工焊条电弧焊和熔化极活性气体保护焊对超细晶Q460钢进行了焊接,分析表征了焊接接头的组织结构、显微硬度和冲击韧性的变化规律。研究结果表明,采用E5515焊条焊接,焊缝金属主要为先共析铁素体、多边形铁素体与少量珠光体。采用ER55-G焊丝,熔化极活性气体保护焊,焊缝金属主要由针状铁素体和少量多边形铁素体组成,焊丝中Ti元素的添加有利于获得针状铁素体组织。采用较小的焊接线能量,超细晶Q460钢热影响区粗晶区组织为粒状贝氏体组织。焊缝金属的显微硬度高于热影响区和母材的显微硬度,热影响区未出现软化现象。冲击试验表明,焊缝金属和热影响区均具有较高的冲击韧性,而且热影响区的韧性高于焊缝金属的韧性。     

316L/S32101异种金属焊接接头的显微组织与力学性能研究

目的 研究乏燃料水池用钢板316L与覆板S32101双相不锈钢的焊接性、接头不同区域显微组织特征及接头与母材之间的性能差异.方法 利用氩弧焊接技术对5 mm厚的316L底板与3 mm厚的S32101覆板以搭接的形式进行焊接,利用金相显微镜、扫描电镜、维氏显微硬度仪和电子万能材料试验机对焊接接头的宏观形貌、显微组织以及力学性能进行研究.结果 316L/S32101焊缝组织主要由铁素体基体、晶界树枝状奥氏体以及晶内细小片状奥氏体所组成;316L侧靠近焊缝处存在一个较窄的熔合区,其组织由奥氏体基体和少许细小分散的铁素体组成,而S32101侧靠近焊缝处组织则由粗大铁素体晶粒和沿晶粒边界分布的若干小块状奥氏体组成.从316L母材区到焊缝区,硬度显著增大,而从焊缝区到S32101母材区,硬度变化很小;焊接接头的抗拉强度高达510 MPa,为两侧316L和S32101母材强度的87.9％和88.6％.结论 在焊接电流为240 A和焊接速度为300 mm/min的条件下,可以通过氩弧焊获得成形良好的搭接接头,且接头的力学性能优异.     

异种铝合金回填式搅拌摩擦点焊工艺的研究

目的 研究搅拌头转速和轴套下压量对异质铝合金回填式搅拌摩擦点焊接头的组织及力学性能的影响。方法 采用回填式搅拌摩擦点焊技术对7050铝合金和2524铝合金进行搭接焊试验,焊接完成后利用光镜、体式显微镜、扫描电镜对组织进行观察,另外,测试拉伸剪切载荷和显微硬度分布,最后对断裂行为进行了研究。结果 接头区域可以分为焊核区、热力影响区、热影响区、母材4个区域,焊核区晶粒呈细小等轴状,热力影响区晶粒呈粗大长条状。随搅拌头转速的增大,拉剪载荷降低,当转速为1500 r/min时拉剪载荷值最高,其值为7.499 44 kN。热影响区的显微硬度比母材低,最小值为HV106。接头的断裂方式可以分为剪切型断裂、塞型断裂、剪切-半环型断裂。结论 在一定工艺参数范围内,通过适当降低搅拌头转速能显著提高接头的拉剪载荷,轴套下压量对接头的断裂方式影响显著。     

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。     

热输入对Q1100钢焊接接头低温韧性及耐蚀性能的影响

采用10 kJ/cm和15 kJ/cm两种焊接热输入对Q1100超高强钢进行熔化极气体保护焊,研究焊接接头的组织性能及局部腐蚀行为。结果表明：两种热输入焊接接头的焊缝组织主要为针状铁素体和少量的粒状贝氏体,粗晶区组织均为板条贝氏体,细晶区组织均为板条贝氏体和粒状贝氏体,临界相变区组织为多边形铁素体、马奥岛和碳化物的混合组织。两种热输入焊接接头中电荷转移电阻均为母材>热影响区>焊缝区,母材耐蚀性最好,热影响区次之,焊缝区耐蚀性最差。在腐蚀过程中,焊缝区作为阳极最先被腐蚀,当腐蚀一定时间后,腐蚀位置发生改变,阳极腐蚀区域转移到母材区,而焊缝区作为阴极得到保护。热输入为10 kJ/cm时,焊接接头具有更好的低温韧性和耐蚀性,其焊缝和热影响区-40℃冲击功分别为46.5 J和30.2 J。     

Characterization on strength and toughness of welded joint for Q550 steel

Q550 high strength steel was welded using gas shielded arc welding and three different welding wires without pre- or post-heat treatments. The paper investigates the influence of welding wire on the microstructure, tensile strength and impact toughness of Q550 steel weld joints. Results showed that the microstructure of the weld metal of joints produced using ER50-6 wire was a mixture of acicular ferrite and grain boundary ferrite including pro-eutectoid ferrite and ferrite side plate. Acicular ferrite was mainly obtained in the weld metal of the joints produced using MK·G60-1 wire. Pro-eutectoid ferrite was present along the boundary of prior austenite. Crack initiation occurred easily at pro-eutectoid ferrite when the joint was subjected to tensile. Tensile strength and impact toughness were promoted with increasing acicular ferrite. Tensile strength of the joint fabricated using MK·G60-1 wire was close to that of base metal. And tensile samples fractured at location of the fusion zone, which had lower toughness and thus became the weak region in the joint. Impact absorbing energy was the highest in the heat affected zone. Fibrous region in fracture surfaces of impact specimens was characterized as transgranular fracture with the mechanism of micro-void coalescence. Acicular ferrite microstructure region corresponded to relatively large dimples while boundary ferrite microstructure corresponded to small dimples.     

Identification of the pin offset effect on the friction stir welding (FSW) via Taguchi – Grey relational analysis: A Case study for AA 7075 – AA 6013 alloys

The aim of this work is to present a case study relating to the dissimilar friction stir welding (FSW) ability of AA 7075‐T651 and AA 6013‐T6 by applying pin offset technique. An orthogonal array L18 was conducted to perform the overlapped weld seams using three different values of pin offset, welding speed and tool rotational speed along with two different pin profiles determine the impact of welding parameters on the tensile properties of friction stir welded joints. The nugget zone for each of overlapped weld seams exhibited a complex structure and also, the pin offset and profile also were found to have a great impact on the microstructural evolution of the nugget zone. The ultimate tensile strength, elongation at the rapture and bending strength of welded joints were measured in the ranges of 194–215 MPa, 1.79–3.34 % and 203–352 MPa. From the Taguchi based Grey relational analysis, the optimum welding condition was determined for the welded joint performed using a single fluted pin profile with the zero pin offset, tool rotational speed of 630 min^?1 and welding speed of 63 mm/min. Microstructural and macro‐structural observations revealed that welded joints exhibiting lower tensile strength are consistent of various types of defects (e. g. cracks, tunnels and cavities). The fracture location of welded joints was found to be on the heat affected zone and between the heat affected zone and AA 6013‐base metal. The tool and pin wear was not observed during the welding applications     

搅拌摩擦焊对Mg-Gd-Y-Zr合金组织与性能的影响

对一种Mg-Gd-Y-Zr合金cast-T6状态板片试样搅拌摩擦焊接后的组织与性能进行了研究。结果表明:Mg-Gd-Y-Zr合金的搅拌摩擦焊的焊核区发生动态再结晶,为等轴细晶,硬度值最高;热机影响区基体组织具有热变形特征,第二相会粗化、溶解,硬度值稍低;热影响区晶粒尺寸与母材相当,第二相粗化,硬度值低于母材。在本工作实验条件下,cast-T6铸件试样的焊接系数达0.91,且伸长率相对于母材有大幅度提高。断口形貌SEM分析显示,接头断裂模式为韧性断裂。     

Effect of self-support friction stir welding on microstructure and microhardness of 6082-T6 aluminum alloy joint

In this paper, 5-mm-thick 6082-T6 aluminum alloy was joined by means of self-support friction stir welding (SSFSW). Here we report the grain structure and second phase particles in various regions including the welding nugget zone (WNZ), thermo-mechanically affected zone (TMAZ), and heat affected zone (HAZ). In the upper part of the joint, microhardness in the TMAZ in proximity of the UWNZ was the highest (average 89.4 HV) due to the severe plastic deformation. The similar result was also found in the lower part of the SSFSW joint. The microstructural development in each region was a strong function of the local thermo-mechanical cycle experienced during welding. Some coarse equiaxed grains which were produced in incomplete dynamic recrystallization process and dissolution of some precipitates have been observed in TMAZ. The HAZ retained the same grain structure as the base material, however, the grain size decreased with increasing distance of the weld centerline.     

热成形淬火对QP1180/22MnB5激光拼焊板组织与性能的影响

目的 对QP1180和22MnB5激光拼焊板进行热成形试验,以解决超高强钢板材焊后的软化问题。方法 选择QP1180和22MnB5异种高强钢作为母材进行激光自熔焊,对焊后的激光拼焊板进行热成形试验,通过体式显微镜、扫描电子显微镜、液压拉伸试验机和维氏硬度计等手段,分析热成形前后激光拼焊板微观组织和力学性能的变化。结果 与焊态拉伸试样相比,热成形试样抗拉强度提高了135%,断后伸长率降低了55%,拉伸试样都在22MnB5母材处断裂,均为塑性断裂。在热成形后,对焊接接头进行组织分析,发现QP1180母材区马氏体含量增加,22MnB5母材区和临界热影响区组织由珠光体和铁素体转变为马氏体,焊接接头热影响区各亚区的组织均转变为大小不同的板条马氏体。硬度测试结果表明,焊态试样焊接接头的QP1180临界区存在软化现象,硬度值最低为335HV,22MnB5侧硬度值由母材处向焊缝升高,母材硬度最低为170HV;而在热成形后,QP1180临界区软化现象消失,硬度值趋于平缓,22MnB5母材处硬度比焊态试样硬度高了2倍。结论 与焊态试样相比,经热成形后激光拼焊板的焊后软化问题得到了解决。     

Nucleus geometry and mechanical properties of resistance spot welded coated–uncoated DP automotive steels

In this study, mechanical properties of resistance spot welding of DP450 and DP600, galvanized and ungalvanized automotive sheets have been investigated. The specimens have been joined by resistance spot welding at different weld currents and times. Welded specimens have been examined for their mechanical, macrostructure and microstructure properties. Depending on the weld current and time, effects of zinc coating on tensile properties, microhardness values as well as microstructure nugget geometry and nucleus size ratio have been investigated. X-ray diffraction analysis has been used to investigate the phase that formed at the joint interface. Result of the experiment show that nugget diameter, indentation depth and tensile load-bearing capacity are affected by weld parameters. Coating prevents full joining at low parameters. Microhardness increased in heat-affected zone and weld metal.     

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%。     

铝合金超声辅助搅拌摩擦焊接接头组织性能研究

目的探究超声振动对铝合金搅拌摩擦焊的作用效果。方法分别采用普通搅拌摩擦焊和超声辅助搅拌摩擦焊方法,对7075铝合金进行焊接试验,并对焊接接头的微观组织、力学性能、断口形貌进行分析。结果普通搅拌摩擦焊焊缝中生成了隧道型缺陷,施加超声振动后,缺陷消失,形成了无缺陷的良好接头,且与普通搅拌摩擦焊相比,超声辅助搅拌摩擦焊焊缝热影响区晶粒长大程度较小,焊核晶粒细化。接头强度明显提高,达到铝合金母材强度的71.5%,接头断裂模式为韧窝和准解理的混合断裂形式。结论超声振动促进了塑性金属的流动,能有效抑制孔洞、隧道型缺陷等的形成,同时超声振动能在提升金属塑性的同时,降低焊缝的热输入。     

Effect of heat input and weld chemistry on mechanical and microstructural aspects of double side welded austenitic stainless steel 321 grade using tungsten inert gas arc welding process

Stainless steel 321 is a stabilized austenitic grade that prevents the formation of chromium carbides at the grain boundaries and subsequently reduces the risk of corrosion attack at the weld surface by forming titanium carbide. It is primarily used in industries such as pressure vessels, boilers, nuclear reactors, carburetors and car exhaust systems. In order to assess the effect of gas tungsten arc welding process parameters on weld penetration, the proposed Taguchi L₉ orthogonal matrix has been selected with two factors and three levels for welding austenitic stainless steel 321 by adjusting the welding current and welding speed. Bead-on-plate experiments were performed on base metal of 6 mm thick plate by changing the process parameters, and corresponding weld bead measurement and macrostructure images are examined. Maximum depth of penetration −3.3017 mm is achieved with a heat input −1.4058 kJ/mm, i. e., welding current-220 A and welding speed-120 mm/min. Double-side arc welding technique is used to obtain full penetration on 6 mm thick plate. The quality of the weldment was assessed using non-destructive radiography inspection. Mechanical integrity and microstructural characteristics of the weldments were studied using tensile (transverse and longitudinal), bend, impact, microhardness, optical microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction analysis, ferrite number measurement and scanning electron microscope. The results reveal that the double side-tungsten inert gas weldment have better mechanical properties. It is corroborated from the weld metal microstructure that it contains γ-austenite, δ-ferrite and titanium carbides (intermetallic compounds). X-ray diffraction analysis and energy dispersive x-ray spectroscopy plots confirm the increase in the ferrite phase in weld metal. The ferrite measurement results show that the ferrite volume in the base metal and weld metal is 1.2 percent and 6.1 percent respectively. In addition, the higher δ-ferrite volume in the weldment helps in attaining superior mechanical integrity. Fractography shows that the failure mode of the weld metal and the base metal is ductile.     

6005A-T6铝合金搅拌摩擦焊接头组织与力学性能特征

采用光学显微镜、扫描电子显微镜、透射电子显微镜、拉伸实验机和显微硬度计对6005A铝合金搅拌摩擦焊接头的微观组织及力学性能进行了研究。结果表明:焊核区为细小的等轴晶,几乎所有粒子溶于基体;热机械影响区呈现为被拉长的畸变晶粒,且存在大量的位错;热影响区的组织明显粗化,处于过时效状态。与母材相比,搅拌摩擦焊接头的强度及伸长率均有下降趋势,且接头出现软化,最小硬度值出现在前进侧的热影响区内。搅拌头旋转速率为1200r/min、焊接速率为200mm/min时可获得优质接头,抗拉强度达到母材强度的72%,伸长率达到母材的69%。     

Joint properties of friction stir welded AZ31B– H24 magnesium alloy

Abstract

The weldability of friction stir welded hot rolled AZ31B-H24 magnesium alloy sheet, 4 mm in thickness, was evaluated, varying welding parameters such as tool rotation speed and travel welding speed. Sound welding conditions depended mainly on sufficient heat input during the welding process. Insufficient heat input, which was generated in the case of higher travel speed and lower rotation speed, caused an inner void or lack of bonding in the stir zone. The microstructure of the weld zone was composed of five regions: base metal, heat affected zone, thermomechanically affected zone, stir zone I and stir zone II. Unlike the general feature of friction stir welded aluminium alloys, the grain size of the weld zone was larger than that of the base metal. Stir zones I and II were characterised by partial dynamic recrystallisation and full dynamic recrystallisation, respectively. The hardness of the weld zone was lower than that of the base metal owing to grain growth. A wider range of defect free welding conditions was acquired at higher tool rotation speed and lower welding speed. The maximum tensile strengh was 240 MPa, which was ~85% of the base metal value of 293 MPa. The fracture location was close to the stir zone.     

S275低合金钢焊接接头的组织与力学性能

通过拉伸、冲击、硬度测试和金相检验等方法对S275低合金钢熔化极活性气体保护焊(MAG)焊接接头的力学性能与显微组织进行了研究。结果表明:采用JM一56焊丝对S275低合金钢进行焊接时,接头具有较好的抗剪强度;开45。坡口,拉伸后均断在离焊缝位置较远的母材上,焊接接头抗拉强度满足技术要求。焊缝组织晶内为细小密集的针状铁素体,有极少量珠光体,焊缝局部有魏氏组织;熔合区、过热区为沿晶界析出的块状先共析铁素体和向晶内生长的条状铁素体以及少量的珠光体;正火区组织为细小的铁素体和珠光体;母材组织为铁素体和珠光体,晶粒也比较细小。最后得出S275低合金钢用于转向架焊接构架是可行的。     

Effect of cooling rate on microstructure,inclusions and mechanical properties of weld metal in simulated local dry underwater welding

Quenched and tempered E550 steel was joined using flux-cored arc welding. The effect of cooling rate on microstructure, inclusions and mechanical properties of the weld metal was investigated by optical microscope, scanning electron microscope, transmission electron microscope and mechanical testing. Results show that weld metal microstructures consist of proeutectoid ferrite, ferrite side plate and acicular ferrite. As the cooling rate increased, the volume fraction of proeutectoid ferrite and ferrite side plate decreased, acicular ferrite increased accompanied with refined grain. Furthermore, inclusions of Ti, Mn oxide with diameter below 2.0 μm were found in the weld metal and rapid cooling rate causes distinct Mn-depleted zone between inclusions and matrix. Excellent balance of high strength and toughness is obtained as more acicular ferrite in weld metal with rapid cooling rate. This can attribute to the increased of acicular ferrite with its refined grain and high density dislocation. These findings suggest that the rapid cooling rate can improve the impact toughness and tensile strength of weld metal in local dry underwater welding.     

汽车高强钢SG1000激光复合焊接力学性能研究

目的 针对汽车高强钢SG1000焊接接头恶化等问题,研究了SG1000激光复合焊接的力学性能。方法 选用等强匹配焊丝MG90-G对高强钢SG1000进行激光复合焊接,对焊接接头进行拉伸和低温冲击韧性试验,并结合扫描和硬度监测等手段对焊缝组织和断口形貌进行分析。结果 由于激光的预热作用,高强钢SG1000激光复合焊接成形件的焊缝美观,焊接过程稳定可靠,焊接熔池深度较大,有效改善了传统焊接的咬边、飞溅、气孔等缺陷。焊缝组织主要由板条马氏体和奥氏体晶粒组成,热影响区的过热区内部板条马氏体和奥氏体晶粒比较粗大,而焊接母材主要为细小的板条马氏体和奥氏体晶粒。焊接拉伸断口主要为细小且较浅的韧窝,且韧窝底部存在第二相粒子及夹杂物,焊接拉伸断口断裂于热影响区且微观形貌为韧性断裂;冲击微观形貌主要由准解理小平面及河流花样组成,且存在一定数量大小不一的韧窝交错分布,焊接冲击断口断裂于热影响区且微观形貌也为韧性断裂。结论 焊缝热影响区的晶粒比非热影响区的晶粒粗大,拉伸和冲击断裂均发生于热影响区;随着激光功率的增大,复合焊接接头的力学性能呈现逐渐增强的趋势;随着焊接速度的增大,复合焊接接头的力学性能呈现先增强后削弱的趋势。高强钢SG1000激光复合焊接最佳工艺参数如下:激光功率为9.5 kW,焊接速度为0.8 m/min,对应屈服强度为1 072 MPa,抗拉强度为1 175 MPa,断裂伸长率为13.5%,冲击断裂吸收的能量为30.8 J、焊缝中心显微硬度为342 HV。