激光焊接钢铝金属间化合物力学性质及组织性能探析

钢铝金属是汽车生产制造中的主要材料,属于轻质化材料,与汽车制造轻质化的发展方向相互吻合,因此,已经成为今后材料使用的主要发展方向。在实际焊接中,由于钢铝之间的性能差异较为明显,因此,在焊接中非常容易形成脆性金属间化合物,为了实现二者之间的高效焊接,需要采取激光焊接技术。基于此,首先,确定激光焊接技术的运用要点。其次,分析钢铝金属间化合物力学性质。最后,研究其组织性能,保证焊接质量的同时,为今后钢铝金属综合性能的提升提供条件。

铝钢金属间化合物生长及其抑制机理的研究现状

铝钢复合材料兼具钢良好的力学性能和铝的耐腐蚀、高导热性、密度低等特点,可以满足许多特殊使用要求。铝钢界面若生成金属间化合物,会破坏铝钢基体间的冶金结合,严重影响材料的使用性能。因此,抑制铝钢界面金属间化合物的生长是开发铝钢复合材料的关键。对铝钢金属间化合物的生长及其抑制机理进行了较为系统的综述,介绍了铝钢界面常见的金属间化合物生成相的种类、晶体结构,从热力学与动力学角度对金属间化合物的生成机理及形成顺序进行了阐述。此外,对比总结了不同合金元素对铝钢金属间化合物形成的影响规律,着重分析了Si元素对铝钢金属间化合物生长的抑制机理。

高强度无碳化物贝氏体钢碳当量公式应用探讨

研究了强度为1 200 MPa级无碳化合物贝氏体钢的焊接冷裂纹的敏感性,结果表明,具有贝氏体铁素体和奥氏体组织的低碳无碳化物贝氏体钢具有较小的焊接冷裂纹敏感性,焊接性良好。从焊接热循环过程焊接接头组织的转变分析了无碳化物贝氏体钢具有较低裂纹敏感性的原因,讨论并提出了适合于无碳化物贝氏体钢碳当量的计算公式。

Effect of intermetallic compounds on heat resistance of hot roll bonded titanium alloy-stainless steel transition joint

The effect of intermetallic compounds on the heat resistance of transition joint was investigated. The experiment of post-weld heat treatment for the hot roll bonded titanium alloy-stainless steel joint using nickels interlayer was carried out, and the interface microstructure evolution due to heat treatment was presented. There was not found significant interdiffusion at stainless steel/nickel interface, when the specimens were heat treated in the temperature range of 600-800 °C for 10 and 30 min, while micro-cracks occurred at the stainless steel/nickel interface heat treated at 700 °C for 30 min. The thickness of intermetallic layers at nickel/titanium alloy interface increased at 600 °C, and micro-cracks occurred at 700 and 800 °C. The micro-cracks occurred between intermetallic layers or between intermetallic layer and nickel interlayer as well. The tensile strength of the transition joint decreased with the increase of heat treatment temperature or holding time.

Effects of welding parameters and tool geometry on properties of 3003-H18 aluminum alloy to mild steel friction stir weld

Defect-free butt joints of 3003 Al alloy to mild steel plates with 3 mm thickness were performed using friction stir welding （FSW）. A heat input model reported for similar FSW was simplified and used to investigate the effects of welding speed, rotation speed and tool shoulder diameter on the microstructure and properties of dissimilar welds. The comparison between microstructure, intermetallics and strength of welds shows the good conformity between the results and the calculated heat input factor （HIF） achieved from the model. The joint strength is controlled by Al/Fe interface at HIF of 0.2-0.4, by TMAZ at HIF of 0.4-0.8 and by intermetallics and/or defects at HIF0.8.

Microstructure evolution and corrosion behavior of Fe-Al-based intermetallic aluminide coatings under acidic condition

Two Fe-Al-based intermetallic aluminide coatings were fabricated on 430-SS(Fe-Cr)and 304-SS(Fe-Cr-Ni)substrates by pressure-assisted solid diffusion bonding with coating on pure Fe as control.The microstructure and intermetallic phases of the coatings were characterized by SEM,EDS and EBSD.A network of Cr2Al13 with matrix of Fe4Al13 was formed by inter-diffusing of Al with the substrates.The corrosion behavior of intermetallic coatings was investigated in 0.5 mol/L HCl solution by mass-loss,OCP,Tafel plot and EIS.It was found that corrosion resistance was greatly enhanced by dozens of times after the addition of Cr and Ni compared with that on pure Fe.The presence of cracks in the coating on 430-SS provided a pathway for corrosion media to penetrate to the substrate and accelerated the corrosion rate.Moreover,the corrosion product was analyzed by XRD,demonstrating that the addition of Cr and Ni facilitated the formation of more corrosion resistant phases,and therefore improved corrosion resistance.

Effect of Mg and Si on intermetallic formation and fracture behavior of pure aluminum-galvanized carbon-steel joints made by weld-brazing

Commercial pure aluminum and galvanized carbon steel were lap-welded using the weld-brazing(WB)technique.Three types of aluminum filler materials(4043,4047,and 5356) were used for WB.The joint strength and intermetallic compounds at the interface of three series of samples were analyzed and compared.Depending on the Si content,a variety of ternary Al-Fe-Si intermetallic compounds(IMCs) such as Fe_(4)(Al,Si)_(13),Fe_(2) Al_(8) Si(τ_(5)),and Fe_(2) Al_(9) Si_(2)(τ_(6)) were formed at the interface.Mg element in 5356 filler material cannot contribute to the formation of Al-Fe intermetallic phases due to the positive mixing enthalpy of Mg-Fe.The presence of Mg enhances the hot cracking phenomenon near the Al-Fe intermetallic compound at the interface.Zn coating does not participate in intermetallic formation due to its evaporation during WB.It was concluded that the softening of the base metal in the heat-affected zone rather than the IMCs determines the joint efficiency.

Effect of Si content on interfacial reaction and properties between solid steel and liquid aluminum

The effect of Si content on the microstructures and growth kinetics of intermetallic compounds(IMCs)formed during the initial interfacial reaction(<10 s)between solid steel and liquid aluminum was investigated by a thermophysical simulation method.The influence of Si addition on interfacial mechanical properties was revealed by a high-frequency induction brazing.The results showed that IMCs layers mainly consisted ofη-Fe_(2)Al_(5)andθ-Fe_(4)Al_(13).The addition of Si reduced the thickness of the IMCs layer.The growth of theηphase was governed by the diffusion process when adding 2 wt.%Si to the aluminum melt.When 5 wt.%or 8 wt.%Si was added to aluminum,the growth was governed by both the diffusion process and interfacial reaction,and ternary phaseτ1/τ9-(Al,Si)_(5)Fe_(3)was formed in theηphase.The apparent activation energies of theηphase decreased gradually with increasing Si content.The joint with pure aluminum metal had the highest tensile strength and impact energy.

Adsorption isotherm mechanism of amino organic compounds as mild steel corrosion inhibitors by electrochemical measurement method

The inhibition ability of 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol （APTT）, ethylenediaminetetra-acetic acid （EDTA） and thiourea （TU） for mild steel corrosion in 1.0 moFL HC1 solution at 30 ℃ was investigated. Tafel polarization and electrochemical impedance spectroscopy （EIS） were used to investigate the influence of these organic compounds as corrosion inhibitors of mild steel in 1.0 mol/L HC1 solution at 30 ℃. The inhibition mechanism was discussed in terms of Langrnuir isotherm model. Results obtained from Tafel polarization and impedance measurements are in a good agreement. The inhibition efficiency increases with the increase of the inhibitor concentration. The adsorption of the inhibitors on the mild steel surface follows Langmuir adsorption isotherm and the free energy of adsorption AGads indicates that the adsorption of APTT, EDTA, and TU molecules is a spontaneous process and a typical chemisorption.

Intergranular Corrosion of AISI 304 Heat Treated at 800℃ Varying Range Times

Austenitic stainless steels, when exposed to welding conditions or aging for length of service, it＇s observed the formation of numerous deleterious phases, such as several kinds of carbides type MC, M6C, M7C3, M23C6, and intermetallic secondary phases （sigma, chi, laves）, which cause the process of intergranular corrosion. The aim of this work was verifying the formation of the types of carbides and/or intermetallic phases existing in the stainless AISI 304 at 800 ℃, varying the timing of heat treatment between 30, 360 and 1,440 min. The optical microscopy analysis revealed the predominant formation of the carbide type M23C6. The results of DL-EPR （double loop electrochemical potentiokinetic reactivation） tests showed a gradual increase in the precipitation of this carbide with the increase of treatment time. The potentiodynamic polarization showed that the precipitation of this carbide reduce the formation of the Cr2O3 passive layer, suggesting that the precipitate carbide to be predominantly of the Cr23C6 type.

Chloride Stress Corrosion Cracking of 316 Austenitic Stainless Steel

SCC （stress corrosion cracking） is environmentally well-known as a failure caused by exposure to a corroding while under a sustained tensile stress. SCC is most often rapid, unpredictable. Failure can occur in a short time as a few hours or take years and decades to happen. Most alloys are liable to SCC in one or more environments requiring careful consideration of alloy type in component design. In aqueous chloride environments austenitic stainless steels and many nickel based alloys are common to perform poorly. SCC of austenitic stainless steels of types 316 was investigated as a function of applied stress at room temperature in sodium chloride solutions using a constant load method. The experiment uses a spring loaded fixture type and is based on ASTM G49 for experiment method, and E292 for geometry of notched specimen. The stress depends on fracture appearance and parameters of time to cracking, and cracking growth. The results explained in terms of comparison between the two concentrations of sodium chloride solutions.