Research on microstructure and properties of boron/Q235 steel laser welded dissimilar joints under synchronous thermal field

The mechanical mismatch effect frequently occurs in the dissimilar materials welded joints, thus leading to plastic gradient at the interface between the weld and heat-affected zone(HAZ). In this work, the boron steel and Q235 steel were selected for laser tailor welding,which obtained boron/Q235 steel tailor-welded blanks(TWBs). The method of welding with synchronous thermal field(WSTF) was utilized to eliminate the mismatch effects in TWBs. The WSTF was employed to adjust cooling rates of welded joints, thereby intervening in the solidification behaviors and phase transition of the molten pool. Boron/Q235 steel was welded by laser under conventional and WSTF(300-600 ℃) conditions, respectively. The results show that the microstructure of weld and HAZ(boron) was adequately transitioned to ferrites and pearlites instead of abundant martensite by WSTF. Meanwhile, the discrepancy of microhardness and yield strength between various regions of welded joints was greatly reduced, and the overall plasticity of welded joints was enhanced by WSTF. It is indicated that WSTF can effectively contribute to reducing plastic gradient and achieving mechanical congruity in welded joints by restraining the generation of hardbrittle phase, which could significantly improve the formability of TWBs in subsequent hot stamping.

Deformation behavior of laser bending of circular sheet metal

The application of a thermal source in non-contact forming of sheet metal has long been used. However, the replacement of this thermal source with a laser beam promises much greater controllability of the process. This yields a process with strong potential for application in aerospace, shipbuilding, automobile, and manufacturing industries, as well as the rapid manufacturing of prototypes and adjustment of misaligned components. Forming is made possible through laser-induced non-uniform thermal stresses. In this letter, we use the geometrical transition from rectangular to circle-shaped specimen and ring-shaped specimen to observe the effect of geometry on deformation in laser forming. We conduct a series of experiments on a wide range of specimen geometries. The reasons for this behavior are also analyzed. Experimental results are compared with simulated values using the software ABAQUS. The utilization of line energy is found to be higher in the case of laser forming along linear irradiation than along curved ones. We also analyze the effect of strain hindrance. The findings of the study may be useful for the inverse problem, which involves acquiring the process parameters for a known target shape of a wide range of complex shape geometries.

Heat-treated microstructure and mechanical properties of laser solid forming Ti-6Al-4V alloy

The effects of heat treatment on the microstructure and mechanical properties of laser solid forming （LSF） Ti-6Al-4V alloy were investigated The influences of the temperature and time of solution treatment and aging treatment were analyzed. The results show that the microstructure of LSFed samples consists of Widmanstatten α laths and a little acicular in columnar prior β grains with an average grain width of 300 μm, which grow epitaxiaUy from the substrate along the deposition direction （27）. Solution treatment had an important effect on the width, aspect ratio, and volmne fraction of primary and secondary a laths, and aging treatment mainly affects the aspect ratio and volume fraction of primary α laths and the width and volume fraction of secondary a laths. Globular a phase was first observed in LSFed samples when the samples were heat treated with solution treatment （950℃, 8 h/air cooling （AC）） or with solution treatment （950℃, 1 h/AC） and aging treatment （550℃, above 8 h/AC）, respectively. The coarsening and globularization mechanisms of a phase in LSFed Ti-6Al-4V alloy during heat treatment were presented. To obtain good integrated mechanical properties for LSFed Ti-6Al-4V alloys, an optimized heat treatment regimen was suggested.

Effect of laser power and deposition environment on the microstructure and properties of direct laser metal-deposited 12CrNi2 steel

Direct laser metal deposition was used for preparing blocks of steel 12CrNi2 using four different laser powers under two different deposition environments including atmospheric environment and Ar-protected chamber.The results showed that microstructures and mechanical properties were significantly affected by different laser powers.Increasing laser power and deposition in Ar chamber will lead to a decrease in the quantity and size of the voids,which brings more elongation to the samples.Bainitic microstructure was replaced by Widmanstatten ferrite and pearlite,and the amount of proeutectoid ferrite increased with increasing laser power.Moreover,microstructures of previous layers were completely altered in high laser power.Excessive heat accumulation by using high heat input can produce equiaxed ferritic grains with the pearlites in previously deposited layers.Hardness of deposited samples increased from the bottom layer toward the top layer.By using a diode laser with a spot diameter size of 2 mm,the 900-W laser power is suitable for producing crack-and void-free samples.However,post-deposition heat treatment is necessary for obtaining homogeneous desired microstructure and grain size in the manufactured samples.

Laser Additive Manufacturing on Metal Matrix Composites: A Review

Important progresses in the study of laser additive manufacturing on metal matrix composites(MMCs)have been made.Recent efforts and advances in additive manufacturing on 5 types of MMCs are presented and reviewed.The main focus is on the material design,the combination of reinforcement and the metal matrix,the synthesis principle during the manufacturing process,and the resulted microstructures as well as properties.Thereafter,the trend of development in future is forecasted,including:Formation mechanism and reinforcement principle of strengthening phase;Material and process design to actively achieve expected performance;Innovative structure design based on the special properties of laser AM MMCs;Simulation,monitoring and optimization in the process of laser AM MMCs.

Research on the Formation of Metal-Ceramic Surface Composite Coating by Wide-Band Laser Cladding

Large-area in-situ synthesized TiB2(TiB, Fe2B)—Fe metal-ceramic composite coating has been fabricated on medium carbon steel by laser cladding with the optimal laser parameters and overlapping coefficient. The bonding interfaces between the cladding layer and the matrix and among different tracks are excellent. Microanalysis on the cladding layer shows that the morphology is a little different from each other and the element distribution and the mechanical properties are unanimous in each track while the mechanical property of the cladding layer shows a gradual change from the surface to the matrix. The in-situ separating out thin ceramic phases in the coating contribute to the improving of its properties greatly.

In-situ formation of Ti-Mo biomaterials by selective laser melting of Ti/Mo and Ti/Mo_(2)C powder mixtures:A comparative study on microstructure,mechanical and wear performance,and thermal mechanisms

Ti-Mo alloys/composites are expected to be the next-generation implant material with low moduli but without toxic/allergic elements.However,synthesis mechanisms of the Ti-Mo biomaterials in Selective Laser Melting(SLM)vary according to raw materials and fundamentally influence material performance,due to inhomogeneous chemical compositions and stability.Therefore,this work provides a comparative study on microstructure,mechanical and wear performance,and underlying thermal mechanisms of two promising Ti-Mo biomaterials prepared by SLM but through different synthesis mechanisms to offer scientific understanding for creation of ideal metal implants.They are(i)Ti-7.5 Mo alloys,prepared from a conventional Ti/Mo powder mixture,and(ii)Ti-7.5 Mo-2.4 Ti C composites,in-situ prepared from Ti/Mo_(2)C powder mixture.Results reveal that the in-situ Ti-7.5 Mo-2.4 Ti C composites made from Ti/Mo_(2)C powder mixture by SLM can produce 61.4%moreβphase and extra Ti C precipitates(diameter below 229.6 nm)than the Ti-7.5 Mo alloys.The fine Ti C not only contributes to thinner and shorterβcolumnar grains under a large temperature gradient of 51.2 K/μm but also benefits material performance.The in-situ Ti-7.5 Mo-2.4 Ti C composites produce higher yield strength(980.1±29.8 MPa)and ultimate compressive strength(1561.4±39 MPa)than the Ti-7.5 Mo alloys,increasing by up to 12.1%.However,the fine Ti C with an aspect ratio of 2.71 dominates an unfavourable rise of elastic modulus to 91.9±2 GPa,44.7%higher than the Ti-7.5 Mo alloys,which,nevertheless,is still lower than the modulus of traditional Ti-6 Al-4 V.While,Ti C and its homogeneous distribution benefit wear resistance,decreasing the wear rate of the in-situ Ti-7.5 Mo-2.4 Ti C composites to 6.98×10^(-4)mm^3 N^(-1)m^(-1),which is 36%lower than that of the Ti-7.5 Mo alloys.Therefore,although with higher modulus than the Ti-7.5 Mo alloys,the SLM-fabricated in-situ Ti-7.5 Mo-2.4 Ti C composites can expect to provide good biomedical application potential in cases where combined good strength and wear resistance are required.

Cu/V复合中间层对TC4/IN718激光焊接接头组织及性能的影响

为了实现TC4钬合金与GH4169镍基高温合金的有效连接.采用Cu/V复合中间层对TC4和IN718合金进行连续激光焊接,并分析添加中间层对接头裂纹、组织及力学性能的影响机制.结果表明,常规激光焊接时,TC4/IN718接头焊缝区产生大量Ti-Ni脆性金属间化合物,导致接头形成大量纵向裂纹,焊缝组织为Ti(s,s)+Ti_(2)Ni+Ti-Cr+NiTi+Ni_(3)Ti+Cr(s,s).当采用Cu/V复合中间层后,实现了TC4与IN718合金的有效连接,接头抗拉强度达到271MPa,焊缝组织转变为Ti(s,s)+V(s,s)+NiV_(3)+Cr(s,s)+Cu(s,s)+未熔铜。

超高速激光金属沉积增材制造K648高温合金的显微组织与性能

采用一种新型的超高速激光金属沉积工艺以提高高铬高温合金的制造效率。分别使用透射电子显微镜、拉伸试验机、磨损试验机和电化学工作站对超高速激光金属沉积高铬K648高温合金的析出相生长行为、高温力学性能、耐磨性和耐腐蚀性进行研究,并与传统激光金属沉积工艺进行比较。结果表明,超高速激光金属沉积K648合金的析出相尺寸明显小于传统激光金属沉积工艺制备的K648合金,700℃下的高温强度更高,且具有良好的耐磨性和耐腐蚀性。总之,超高速激光金属沉积制造的K648高铬高温合金具有良好的综合性能。

激光功率对铝/铜激光熔钎焊接头组织及性能的影响

采用激光熔钎焊方法对5052铝合金和T2紫铜进行对接试验,研究了激光功率(2000,2200,2400,2600,2800 W)对接头显微组织和力学性能的影响。结果表明:不同激光功率下接头铜侧钎焊区组织均以柱状晶为主,随着激光功率的增加,焊缝区树枝晶由细针状转变为雪花状;铜侧钎焊区由界面层和金属间化合物层组成,2000,2600 W激光功率下的界面层主要为AlCu相,金属间化合物层主要为Al_(4)Cu_(9)相,2400 W激光功率下的界面层主要由AlCu相和CuZn相组成,金属间化合物层主要为CuZn_(5)相;焊缝区主要由Al_(4.2)Cu_(3.2) Zn_(0.7)和Al_(0.71)Zn_(0.29)相组成。随着激光功率的增加,金属间化合物层厚度增加。激光功率对铜侧钎焊区的显微硬度影响较大,各接头的最高显微硬度均出现在铜侧钎焊区。随着激光功率的增加,接头最高硬度增加,抗拉强度先增大后减小;当激光功率为2400 W时,接头的抗拉强度最大,达到铝合金母材的92%,此时接头在靠近铝合金母材处断裂,而其他激光功率下制备的接头均在铜侧钎焊区和焊缝区处断裂。

316L不锈钢薄板焊缝成形及力学性能研究

目的减少1 mm厚度316L不锈钢薄板在焊接生产过程中出现的缺陷等问题,并提高不锈钢薄板焊缝成形质量和焊接接头力学性能。方法采用脉冲激光焊接技术实现对厚度1 mm的316L不锈钢薄板的精确焊接,并利用金相显微镜、维氏硬度计、万能拉伸试验机和扫描电镜对焊缝的表面形貌、微观结构、力学性能、断口形貌进行表征分析。结果当激光功率为403 W、输出电流为150 A、焊接速度为150 mm/min、离焦量为−5.525 mm时,焊缝正反面的形貌规则无缺陷。焊缝区内的微观结构主要由δ-铁素体和奥氏体2种晶粒构成,相较于母材及热影响区,焊缝区晶粒尺寸更细小均匀,平均硬度为156HV,表现出更高的硬度特性。焊接接头的抗拉强度和屈服强度均值分别达到643.28 MPa和305.95 MPa,相对于母材的强度分别提高了7%和49%;平均断后伸长率为37.2%,达到原始母材伸长率的55%;断裂呈现韧性断裂的塑性变形和延展性特征。结论优化调整焊接工艺参数后,1 mm厚度316L不锈钢薄板的焊缝成形质量提高,无缺陷且微观组织分布均匀,焊接接头强度显著提高。

单晶合金激光增材修复接头组织和性能研究

采用激光熔化沉积技术对DD6单晶高温合金进行修复,利用光学显微镜、扫描电镜和显微硬度仪对单晶母材和增材修复接头的组织特征和力学性能进行对比研究。结果表明:激光熔化沉积修复组织为外延生长的定向凝固柱状晶组织,由γ相基体和少量晶间MC型碳化物组成;DD6单晶合金基体热影响区微观形貌和物相组成与母材相似,但其γ′相的尺寸(≤0.2μm)更小,且γ′/γ的比例明显降低。经激光熔化沉积修复后,增材修复区的显微硬度可达450~470 HV,显著高于DD6单晶基体,具有更优异的耐磨损性能。

Cu含量对激光选区熔化CoCrMoCu合金微观组织及表面摩擦磨损性能的影响

目的阐明不同Cu含量对激光选区熔化(Selective Laser Melting,SLM)制备的CoCrMoCu合金微观组织的影响及其在表面摩擦磨损和腐蚀性能使役行为方面的作用。方法采用CoCrMo合金粉和纯Cu粉通过行星球磨机进行机械混合,制备了Cu质量分数为2%、4%、6%的CoCrMo/Cu混合粉末,并通过SLM技术制备相应的试样。对不同Cu含量的SLM CoCrMoCu的相组成、微观结构、硬度、摩擦磨损和腐蚀性能进行检测和分析。结果Cu含量对SLM CoCrMoCu的相组成和微观组织没有明显影响,在不同Cu含量的试样中,试样的微观组织均主要为胞状等轴晶。在力学性能方面,随着Cu含量的升高,试样的硬度先提升后降低,在含2%Cu的情况下达到最大值(429.2HV0.2),在含6%Cu的情况下达到最小值(367.7HV0.2)。CoCrMoCu的摩擦因数和磨损率随着Cu含量的升高而降低,在4%时摩擦因数和磨损率达到最低(2.7×10^(-5)mm^(3)/(N·m)),摩擦磨损性能最好。随着Cu质量分数进一步增加到6%,由于硬度降低,磨损性能下降,试样表面出现沟壑,影响Cu自润滑层的附着,磨损机制由黏着磨损向磨粒磨损转变,导致摩擦因数和磨损率增加。在腐蚀性能方面,腐蚀电位随着Cu含量的升高而升高,而腐蚀电流随着Cu含量的升高呈现先下降后上升的趋势,在4%时达到最佳的腐蚀性能。结论Cu的引入在一定范围内(2%~4%)可以有效提高CoCrMoCu合金的硬度和腐蚀性能。结合Cu的自润滑效应和类钝化效应,实现CoCrMo合金耐磨性能和腐蚀性能的协同提升。

窄孔内壁激光金属沉积Stellite6合金耐磨层组织及性能研究

为解决窄孔内壁堆焊的可达性差和提高304L不锈钢的耐磨性能,采用激光金属沉积的方式在深30 mm、直径14 mm的304L窄孔内壁制备了一层约2.5 mm厚、致密度为99.9981%、无裂纹、未熔合等缺陷的stellite6耐磨层。通过微纳CT、XRD、金相、硬度测试和摩擦磨损试验等方法,系统研究了耐磨层的组织、相组成、硬度分布和耐磨性能。结果表明,Stellite6耐磨层致密无缺陷,其显微组织从底部到顶部依次为平面晶、胞状晶、树枝晶和等轴晶。相组成主要为γ-Co、M_(23)C_(6)、CoCx及(Cr,Fe)_(7)C_(3)等。熔合线附近各种元素均匀分布,未出现明显聚集。耐磨层的显微硬度平均值是基体304L的2.38倍,且窄孔不同高度位置的显微硬度值相对稳定。耐磨层的磨损率较304L基体降低了29.3%,显示出优异的耐磨性能。该研究为大深宽比内孔壁激光金属沉积耐磨层在核电、能源动力等行业的应用提供了依据。

316L不锈钢超薄板激光焊接头微观组织及力学性能研究

为了探索316L不锈钢超薄板在换热器、金属极板等领域的应用,采用脉冲激光器对0.15 mm厚316L不锈钢板进行激光焊接工艺实验,并对焊接接头的微观组织和力学性能进行了分析。结果表明:当激光功率为90W、焊接速度为25 mm/s、脉冲频率为90 Hz、激光焦距为-1.5 mm时,能够得到单面焊双面成型、表面光滑无缺陷的焊接接头。焊缝区由细小的等轴晶组成,硬度高于母材区的,焊接接头的抗拉强度约为539.5 MPa,达到母材的86.8%,断后伸长率约为30.5%,达到母材的75.7%。

Q235钢薄板激光焊接头微观组织与力学性能

为了探索光纤激光在焊接薄板低碳钢中的应用前景,文中采用光纤激光焊接系统分别对0.5 mm和1 mm厚Q235钢板进行了激光焊工艺试验,并对所得到的焊接接头的微观组织和力学性能进行了分析。通过调节激光功率、摆动频率等工艺参数,2种厚度的Q235钢板均可获得单面焊双面成形、无明显缺陷的焊接接头。厚0.5 mm板焊缝区主要由板条马氏体组成,硬度和抗拉强度均高于母材的,断后伸长率为33.1%,约为母材的79%;厚1 mm板焊缝区呈胞状树枝晶组织,主要由铁素体、珠光体和贝氏体组成,硬度和抗拉强度均高于母材的,断后伸长率为34.5%,约为母材的75%。

超声振动辅助铝/钢激光–MIG熔钎焊外观成形、组织以及拉伸性能研究

目的利用超声振动改善铝/钢对接接头界面的微观结构,降低气孔缺陷并提高接头力学性能。方法通过超声振动辅助激光–MIG焊接方法实现铝/钢异种金属连接,采用光学显微镜观察焊缝形貌,采用金相显微镜和扫描电子显微镜观察焊缝和界面微观结构,利用拉伸试验机测试接头的拉伸强度。结果超声振动的施加提高了熔融金属的润湿铺展性能,减少了焊缝中的气孔缺陷,并降低了界面层金属间化合物的厚度。带有余高和去除余高的接头拉伸强度由未加超声的175 MPa和154 MPa分别提高到189 MPa和172 MPa。结论利用超声振动的声流、空化效应有效改善了熔融金属的润湿铺展性能和界面微观结构,并在一定程度上消除了气孔缺陷,进而提高了接头的力学性能。

镀锌钢板激光填丝焊接工艺与接头力学性能研究

车身用镀锌钢板的厚度较薄,采用其他方法焊接制造容易产生较大变形,开发厚度较薄的镀锌钢板激光填丝焊接工艺具有重要工程实践意义。针对车身用0.7 mm厚异种镀锌钢板,开展激光填丝焊接工艺试验,系统研究关键工艺参数(激光功率、焊接速度、离焦量和送丝速度)对焊缝表面和横截面的影响规律,分析焊接接头的微观组织特征和力学性能。结果表明,激光功率、焊接速度、离焦量和送丝速度有较好匹配时,可以获得焊接飞溅少、表面光滑的焊缝;焊接接头拉伸试样在强度较弱的母材发生断裂。

钛合金板料激光曲线弯曲及热辐射对其组织性能的影响

研究了激光能量密度、路径曲率和扫描次数对 ＴＣ４（Ｔｉ－６Ａｌ－４Ｖ）板料弯曲变形的影响规律同时，分析了热辐射对板 料显微组织和表面硬度的影响．结果表明：（１）存在一个最优的能量密度值使板料一次弯曲所获得的弯曲角度达到峰值；（２）随 路径曲率的增加，弯曲角度减小；（３）第一次扫描以后的扫描次数与弯曲角度呈准线性关系；（４）合适的工艺参数不会导致材料显微组织变化，且激光热辐射对材料表面有淬火效应，使加热区材料表面硬度均有所提高．

钢/铝异种金属添加粉末的激光焊接

采用光纤激光器对1.4 mm厚DC51D+ZF镀锌钢和1.2 mm厚6016铝合金平板试件进行添加Mn、Zr粉末的激光搭接焊试验,利用金相显微镜、显微硬度仪、扫描电镜、X射线衍射仪、微机控制电子万能试验机等研究焊接接头各区域的金相组织、显微硬度、断口形貌、主要物相与接头的力学性能。结果表明:在钢/铝激光焊中添加Mn、Zr粉末,焊接接头平均抗剪强度与没有添加粉末相比,有所提高,其中添加Zr粉末的提高效果明显;Mn、Zr粉末的添加改变了钢/铝界面的元素分布、物相组成及微观组织形态,添加Mn能提高熔池金属的流动性,利于钢/铝界面结合,而添加Zr,焊缝区晶粒细小,形成新的ZrFe3.3Al1.3韧性相,抑制Fe-Al脆性金属间化合物生成。因此,添加Mn、Zr均改善了钢/铝焊接接头的力学性能。