Microstructure and Mechanical Properties of Aer Met 100 Ultra-high Strength Steel Joints by Laser Welding

AerMet100 ultra-high strength steel plates with a thickness of 2 mm were welded using a COz laser welding system. The influences of the welding process parameters on the morphology and microstructure of the welding joints were investigated, and the mechanical property of the welding joints was analyzed. The experimental results showed that the fusion zone of welding joint mainly consisted of columnar grains and a fine dendrite substructure grew epitaxially from the matrix. With the other conditions remaining unchanged, a finer weld microstructure was along with the scanning speed increase. The solidification microstructure gradually transformed from cellular crystal into dendrite crystal and the spaces of dendrite secondary arms rose from the fusion line to the center of the fusion zone. In the fusion zone of the weld, the rapid cooling caused the formation of martensite, which led the microhardness of the fusion zone higher than that of the matrix and the heat affected zone. The tensile strength of the welding joints was tested as 1 700 MPa, which was about 87% of the matrix. However, the tensile strength of the welding joints without defects existed was tested as 1832 MPa, which was about 94% of the matrix.

Microstructure and mechanical properties of pulsed laser welded Al/steel dissimilar joint

Pulsed laser welding was used in joining pure aluminum to stainless steel in a lap joint configuration. It is found that the mechanical properties of the laser joints were closely correlated with the bead geometry, i.e., penetration depth. In order to study the correlation, two typical laser welds with different penetration depths were analyzed. In high penetration depth (354 μm) joint, Al-rich Fe?Al IMCs with microcracks were formed at the Al/fusion zone (FZ) interface. The joint strength was found to be (27.2±1.7) N/mm and three failure modes were observed near the Al/FZ interface. In low penetration depth (108 μm) joint, Fe-rich Fe?Al IMCs without any defect were formed at the Al/FZ interface. The joint strength was found to be (46.2±1.9) N/mm and one failure mode was observed across the FZ.

Formation, microstructure and mechanical properties of double-sided laser beam welded Ti-6Al-4V T-joint

The T-joints of Ti?6Al?4V alloy were manufactured by double-sided synchronized laser beam welding with the homologous filler wire. The formation, microstructure and mechanical properties of welded joints as well as the correlations of each other were investigated. The results indicate that the quality of weld seams is good without defects such as discontinuity, beading, visible cracks or porosity, which is linked to the steady molten pool behavior and droplet transition. The morphologies of the heat affected zone (HAZ) located on the skin and stringer are disparate. The microstructure of the HAZ and fusion zone (FZ) is mainly comprised of acicular martensiticα′ phases. The microhardness of the HAZ and FZ is higher than that of the base metal (BM) and reaches a maximum value at the HAZ near FZ on the stringer. The tensile specimens along the skin and stringer fractured at the BM with ductile fracture surfaces.

Effect of Laser Beam Welding Parameters on Microstructure and Properties of Duplex Stainless Steel

The present study is concerned with laser beam welding and its effect on size and microstructure of fusion zone then, on mechanical and corrosion properties of duplex stainless steel welded joints. In this regard, influence of different laser welding parameters was clarified. Both bead-on-plate and autogenously butt welded joints were made using carbon dioxide laser with a maximum output of 9 kW in the continuous wave mode. Welded joints were subjected to visual, dye penetrant and radiography tests before sectioning it for different destructive tests. Accelerated corrosion test was carried out based on tafel plot technique. The results achieved in this investigation disclosed that welding parameters play an important role in obtaining satisfactory properties of welded joint. High laser power and/or high welding speed together with adjusting laser focused spot at specimen surface have produced welded joints with a remarkable decrease in fusion zone size and an acceptable weld profile with higher weld depth/width ratio. Besides, acceptable mechanical and corrosion properties were obtained. Using nitrogen as a shielding gas has resulted in improving mechanical and corrosion properties of welded joints in comparison with argon shielding. This is related to maintaining proper ferrite/austenite balance in both weld metal and HAZ in case of nitrogen shielding. As a conclusion, laser power, welding speed, defocusing distance and type of shielding gas combination have to be optimized for obtaining welded joints with acceptable profile as well as mechanical and corrosion properties.

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.

Microstructure and high-temperature mechanical properties of laser beam welded TC4/TA15 dissimilar titanium alloy joints

The microstructure evolution and high-temperature mechanical properties of laser beam welded TC4/TA15 dissimilar titanium alloy joints under different welding parameters were studied.The results show that the weld fusion zone of TC4/TA15 dissimilar welded joints consists of coarsenedβcolumnar crystals that contain mainly acicularα’martensite.The heat affected zone is composed of the initialαphase and the transformedβstructure,and the width of heat affected zone on the TA15 side is narrower than that on the TC4 side.With increasing temperature,the yield strength and ultimate tensile strength of the TC4/TA15 dissimilar welded joints decrease and the highest plastic deformation is obtained at 800°C.The tensile strength of the dissimilar joints with different welding parameters and base material satisfies the following relation(from high to low):TA15 base material>dissimilar joints>TC4 base material.The microhardness of a cross-section of the TC4/TA15 dissimilar joints reaches a maximum at the centre of the weld and is reduced globally after heat treatment,but the microhardness distribution is not changed.An elevated temperature tensile fracture of the dissimilar joints is located on the side of the TC4 base material.Necking occurs during the tensile tests and the fracture characteristics are typical when ductility is present in the material.

Microstructure and mechanical properties of laser beam welded TC4/TA15 dissimilar joints

The microstructure and mechanical properties of laser beam welded dissimilar joints in TC4 and TA15 titanium alloyswere investigated. The results showed that the coarse columnar grains containing a large amount of acicular α and martensite α′ werepresent in the fusion zone (FZ), some residual α phases and martensite structure were formed in the heat-affected zone (HAZ) onTC4 side, and bulk equiaxed α phase of the HAZ was on TA15 side. An asymmetrical microhardness profile across the dissimilarjoint was observed with the highest microhardness in the FZ and the lowest microhardness in TA15 BM. The orders of yield strengthand ultimate tensile strength were as follows: TC4 BM > TC4/TC4 similar joint > TA15 BM > TA15/TA15 similar joint > TC4/TA15dissimilar joint, and increased while hardening capacity and strain hardening exponent decreased with increasing strain rate from1×10?4 s?1 to 1×10?2 s?1. The TC4/TA15 dissimilar joints failed in the TA15 BM, and had characteristics of ductile fracture atdifferent strain rates.

Microstructures and mechanical properties of laser-welded TiNi shape memory alloy and stainless steel wires

The Nd ： YAG laser welding was used to join the TiNi shape memory alloy and AISI304 stainless steel wires. The microstructural features of the dissimilar material joint were analyzed. The tensile and hardness tests were carried out to examine the mechanical properties and microhardness distribution of the welded joint. The results show that the joint has the non-homogeneous microstructure and element distribution. The brittle phases such as Fe2 Ti , Fe Ti , Cr2 Ti , Ti3 Ni4, Feo 2 Ni4.s Ti5 and TiN mainly segregate in rich Ti region of fusion zone. The laser-welded joint has the tensile strength of 298 MPa with the elongation of 3.72 % and exhibits the brittle fracture features on the fracture surfaces. The reasons for low joint strength were discussed in this investigation.

Effect of W/Cu composite filler metals on the microstructure and mechanical properties of laser welded pure niobium/304 stainless steel joint

Cracking in a laser weld of niobium to stainless steel occurred due to the formation of brittle,continuously distributed Nb-Fe intermetallic compounds.A crack-free joint,which had a tensile strength of 147 MPa,was obtained by using the W/Cu composite filler metals.To determine the reasons for cracking in the Nb/SS joint and the function of the W/Cu composite filler metals on the improvement of the cracking resistance of the Nb/W/Cu/SS joint,the microstructures of the joints were studied by optical microscopy,scanning electron microscopy and X-ray diffraction.The cracking susceptibilities of the joints were evaluated with microhardness test on the cross section of the Nb/W/Cu/SS joint.The results showed that the Nb/W/Cu/SS joint was characterized by various solid solution.The formation of solid solution reduced the cracking susceptibility of the joint.

Effect of laser power on microstructure and mechanical properties of laser heat conduction lap welded joint between AZ31B magnesium alloy and DP780 galvanized steel

In this work, laser heat conduction lap welding(LHCLW) of AZ31B magnesium alloy sheet and DP780galvanized steel sheet was carried out by the defocused laser beam. The effects of laser power on the microstructure and mechanical properties of the joint were studied. The pros and cons of the joint were identified and evaluated by measuring the tensile shear strength, microhardness and microstructure observation. The formation mechanism of various phases at the Mg/steel interface was analyzed. The results indicated that the galvanized layer could promote the metallurgical bonding between magnesium alloy and steel by improving the diffusion ability of molten magnesium alloy at the steel interface and reacting with Mg, so as to enhance the strength of the joint. A continuous dense layered eutectic structure(α-Mg+MgZn) was formed at the interface of the joint, while MgZn_(2)and MgZn phase was formed at the weld edge zone and heat affective zone(HAZ), whereas no reaction layer was generated between the uncoated steel and magnesium alloy. A sound joint could be obtained at 2.5 kW, and the corresponding tensile shear strength reached the maximum value of 42.9 N/mm. The strength was slightly reduced at 2.6 kW due to the existence of microcracks in the eutectic reaction layer.

Microstructures and mechanical properties of dissimilar Nd:YAG laser weldments of AISI4340 and AISI316L steels

This paper presents studies on the microstructure and mechanical properties of AISI 316L stainless steel and AISI 4340 low-alloy steel joints formed by the Nd:YAG laser welding process. The weld microstructures and heat affected zones (HAZs) were investigated. Austenitic microstructures were observed in all of the samples. The sizes of the HAZs changed when the heat input was varied, and the 316L sides exhibited a larger HAZ. The cooling rates were calculated by measuring the solidification dendrite arm spacing. It is shown that high cooling rates lead to an austenitic microstructure. Tensile tests were carried out, and the results revealed the tensile properties of both the base metals and the weldments. The hardness test results agreed well with the tensile test results.

Effect of process parameters on microstructure and properties of laser welded joints of aluminum/steel with Ni/Cu interlayer

The effects of laser parameters and interlayer material on the microstructure and properties of the welded joint between 6061 aluminum alloy and stainless steel were studied.The results show that the density and microstructure of the welded joint can be optimized by changing the laser power with 0.05 mm Cu foil and 0.1 mm Ni foil as interlayer.A large number of new Cu-Al binary phases were found near the aluminum alloy,which effectively inhibited the formation of the binary brittle phase of Fe-Al.The maximum shear force of 1350.96 N was obtained with laser power of 2200 W.The shear force of the welded joint increased to 1754.73 N when the thickness of the Cu foil thickness changed to 0.02 mm.

Microstructure, Mechanical Property and Corrosion Resistance Property of Cr26Mo3.5 Super Ferritic Stainless Joints by P-TIG and Laser Welding

The characteristics of microstructure, mechanical property and corrosion behavior of Cr26Mo3.5 super stainless steel joints by pulse tungsten inert gas(P-TIG)welding and laser welding were investigated. The results indicate that the widths of the center equiaxed grain zone(EGZ)and the columnar grain zone(CGZ)increase with the increase of heat input in both welding processes. The precipitates of Nb and Ti carbides and nitrides are formed in the weld metal(WM)and the heat affected zone(HAZ). The joints by laser welding show better tensile and corrosion resistance properties than those by P-TIG welding due to the heat concentration and lower heat input. The tensile strength and elongation increase with the decrease of heat input, and the fracture mode of the joints turns into ductile-brittle mixed fracture from ductile fracture when the welding method turns into P-TIG welding from laser welding. Moreover, the corrosion resistance of all joints declines slightly with the increase of heat input. Hence, laser welding is more suitable for welding Cr26Mo3.5 super stainless steel in engineering applications.

Metallurgical and Mechanical Properties of Underwater Laser Welds of Stainless Steel

In this paper, the microstructures and mechanical properties of underwater laser welds of Type 304 stainless steel were investigated. JISY308L type filler wire was used as filler wire during welding. A gas-shielding nozzle was used to form a local dry cavity surrounding the welding zone. The main results are summarized as follows: (1) The shielding condition of the local dry cavity severely affects the oxygen content of the weld, the worst shielding condition leading to the oxygen content of 800×10-6, which largely increases the oxide inclusions and somewhat reduces the ferrite content. (2) The increase of oxygen content reduces the elongation rate and reduction of area in tensile test, but has no influence on the tensile strength. (3) In appropriate shielding condition, the mechanical properties of the underwater laser welds can be as same as that in the air.

Effect of Laser Welding Process Parameters on Microstructure and Mechanical Properties on Butt Joint of New Hot-Rolled Nano-scale Precipitation-Strengthened Steel

A 4 kW fiber laser was chosen to weld the new hot-rolled nano-scale precipitation-strengthened steel with a thickness of 4.5 mm. The effect of laser power, defocusing distance, and welding speed on the welded joint appearance was examined, and the microstructure and mechanical properties on the typical butt joints were investigated. Results showed that increasing laser welding power may cause faster downward flow of molten metal to produce greater root humping. With the welding speed increasing, the average welding seam （WS） width decreased, and the average WS and heat-affected zone （HAZ） hardness increased. The microstructures of WS, fusion line, and coarse grain heat-affected zone were lath martensite, but the growth direction of the original austenite grain boundaries was significantly different. The microstructures of fine grain heat-affected zone were ferrite and martensite, and the microstructure of mixed grain heat- affected zone contained ferrite, massive M/A island, and a small amount of martensite. The micro-hardness values of WS, HAZ, and base metal （BM） were 358, 302, and 265 HV, respectively. The butt joint fracture at the BM far from the WS and the welded joint tensile strength are observed to follow proportional relationship with hardness.

An insight into microstructural heterogeneities formation between weld subregions of laser welded copper to stainless steel joints

The effect of laser beam welding(LBW) process on the microstructure-mechanical property relationship of a dissimilar weld between the copper(Cu) and stainless steel(SS) was investigated.Backscattered electron(BSE) based scanning electron microscopy(SEM) imaging was used to characterize the highly heterogeneous microstructural features across the LBW(Cu-SS) weld.The BSE analysis thoroughly evidenced the complex microstructures produced at dissimilar weld interfaces and fusion zone along with the compositional information.Widely different grain growths from coarse columnar grains to equiaxed ultrafine grains were also evident along the Cu-weld interface.A highresolution electron backscattered diffraction(EBSD) analysis confirmed the existence of the grain refinement mechanism at the Cu-weld interface.Both tensile and impact properties of the dissimilar weld were found to be closely aligned with the property of Cu base metal.Microhardness gradients were spatially evident in the non-homogeneous material composition zones such as fusion zone and the Cu-weld interface regions.The heterogeneous nucleation spots across the weld sub-regions were clearly identified and interlinked with their microhardness measurements for a holistic understanding of structure-property relationships of the local weld sub-regions.The findings were effectively correlated to achieve an insight into the local microstructural gradients across the weld.

Microstructure and Mechanical Properties of Galvanized Steel/AA6061 Joints by Laser Fusion Brazing Welding

Laser fusion brazing welding was proposed.Galvanized steel/AA6061 lapped joint was obtained by laser fusion brazing welding technique using the laser-induced aluminium molten pool spreading and wetting the solid steel surface.Wide joint interface was formed using the rectangular laser beam coupled with the synchronous powder feeding.The result showed that the tiny structure with the composition of a-Al and Al–Si eutectic was formed in the weld close to the Al side.And close to the steel side,a layer of compact Fe–Al–Si intermetallics,including the Al-rich FeAl3,Fe2Al5 phases and Al–Fe–Si s1 phase,was generated with the thickness of about 10–20 lm.Transverse tensile shows the brittlefractured characteristic along to the seam/steel interface with the maximum yield strength of 152.5 MPa due to the existence of hardening phases s1 and Al–Fe intermetallics.

Study on laser welded heat-affected zone in new ultralow carbon bainitic steel

800 MPa grade ultralow carbon bainitic （NULCB） steel is the recently developed new generation steel, which was produced by thermo mechanical controlled processing ＆ relaxation-precipitation controlling transformation （TMCP＆RPC） tech- nique. The microstructure and the mechanical properties of the heat-affected zone （HAZ） in NULCB steel under laser welding conditions were investigated by using a Gleeble-1500 thermal simulator. The experimental results indicate that the simplex microstructure in the HAZ is granular bainite that consists of bainite-ferrite （BF） lath and M-A constituent when the cooling time from 800 to 500℃ （t8/5） is 0.3-30 s, and the M-A constituent consists of twinned martensite and residual austenite. As t8/5 increases, the hardness and tensile strength of HAZ decreases, but they are higher than that of the base metal, indicating the absence of softened zone after laser welding. The impact toughness of HAZ increases at first and then decreases when t8/5 increases. The impact energy of HAZ is much higher than that of the base metal when t8/5 is between 3 and 15 s. It indicates that excellent low temperature toughness can be obtained under appropriate laser welding conditions.

Q345B/304异种钢激光填丝焊接工艺与性能研究

为了提高异种钢焊接质量,采用激光焊技术填充ER308L焊丝对Q345B低合金钢与304不锈钢两种异质材料进行焊接。在不同的激光功率下,采用金相显微镜、扫描电镜、能谱仪等对焊接接头进行了深入的表征和分析。结果表明,当激光功率高于3 kW时,接头处得以焊透,4 kW、4.5 kW和5 kW这3种焊缝截面均呈现束腰现象,且焊缝组织均为典型的板条状马氏体,其中5 kW焊接件焊缝所含的板条马氏体更加细小,表现出最高的硬度值;4 kW焊接件的抗拉强度达到590 MPa,随着激光功率的增大,焊接件的抗拉强度逐步下降;焊缝中主要出现了Cr_(2)Ni_(3)、Fe_(2)Ni_(3)、α-Fe等相,没有大量出现对质量有较大影响的M_(23)C_(6)和σ相等有害相。采用激光填丝焊接技术能够实现Q345B/304异种钢的高质量焊接。

不同强度级别双相不锈钢激光焊接头的组织与力学性能

目的为了合理制定不同强度等级DP钢同种和异种接头的激光焊接工艺,研究激光焊接工艺对接头组织性能的影响。方法采用SEM、硬度试验、拉伸试验等手段,研究不同强度等级DP钢同种和异种激光焊接接头的微观组织和力学性能。结果对于同种DP钢激光焊接,由于接头各个区域经历的热循环不同,因此其马氏体体积分数和形态、含碳量等存在明显差异。在焊缝熔合区,由于冷却速度较高,因此马氏体体积分数较高且为细条状,硬度高于母材硬度。在热影响区,由于马氏体发生了回火分解,因此其硬度值低于母材硬度,且软化的程度和范围大小与DP钢的强度级别相关。软化的热影响区成为接头的薄弱区域,降低了接头的拉伸性能。在异种DP钢激光焊接接头中,焊缝熔合区的硬度也明显高于母材硬度。靠近高强度级别母材侧的热影响区范围更大,软化程度更明显,接头硬度分布不再对称。接头的抗拉强度与低等级DP钢母材的抗拉强度基本一致。结论激光焊接工艺对不同强度等级DP钢同种和异种接头组织性能的影响存在较大的差异,DP钢强度级别越高,接头或接头对应侧的热影响区软化程度越明显,这在制定焊接工艺以及焊后处理工艺过程中需要予以考虑。