7A04铝合金锻坯开裂原因分析

7A04铝合金锻坯在锻造过程中发生开裂,通过对锻坯裂纹进行断口宏观及微观观察、能谱分析、金相组织检查,并与人工断口进行对比分析,确定锻坯开裂原因。结果表明:锻坯开裂是由于锻坯内存在金属氧化物夹杂造成的;开裂锻坯断面上存在大量的氧化物夹杂,夹杂物以氧化铁为主,同时含有少量氧化铝和氧化镁。以氧化铁为主的氧化物夹杂的形成应与外来氧化铁坠入熔体被氧化膜包裹有关。     

Improvement of resistance to hydrogen induced cracking in electric resistance welded pipes fabricated with slit coils

The optimization of electric resistance welding (ERW) conditions was studied to improve the resistance to hydrogen induced cracking (HIC) at the bondline in small diameter API X60 ERW pipes fabricated with slit coils. The results show that HIC is initiated preferentially at the elongated Si, Mn and Al-rich oxide inclusions, normally known as a penetrator on the bondline. However, no evidence was found of any centerline segregation effect. The HIC ratio increases with the fraction of penetrators at the bondline, regardless of the degrees of center segregation. Furthermore, for a satisfactory level of HIC resistance, the fraction of penetrators must be less than 0.03 % and most of the penetrators should be circular-shaped. The design of experimental (DOE) method was used to determine the optimum ERW condition for minimization of the penetrator ratio. Finally, guideline is suggested for the optimum ERW condition for achieving excellent HIC resistance.     

Analysis of the effect of deviations in surface preparation technology on the size of internal defects in pulsed-arc welding

Investigations were carried out into the effect of the parameters of pulsed-arc welding on the formation of oxide inclusions when the quality of surface preparation (missing individual areas in grinding) is impaired. The length of the oxide inclusions was estimated on the basis of the ratio of the total length of the oxide films to the length of the welded joint (Σl_f/L_w) and the dispersion was estimated by the deviation of the sum of the lengths of the oxide films to their number (Σl_f/n). The results show that the largest length of the oxide inclusions was obtained at a gap of 1 mm, but the average length of the oxide films in the weld metal is maximum in the gap size range 1.7–2 mm. The increase of the welding speed reduces the total length of the oxide inclusions. The lowest value of the total length of the oxide inclusions in the weld metal and the smallest average dimensions of the films were recorded in pulsed-arc welding in the conditions with ‘hardness’ of the conditions of 0.7 (τ_pulse = 0.3 s, τ_off = 0.21 s).     

The oxidation mechanism in copper smelting and converting

The oxidation mechanism of copper-sulfide concentrates is of fundamental interest in an understanding of flash smelting and converting. The compositions of mattes follow simple, well-defined relationships, and the progression of iron and sulfur oxidation in smelting and converting occurs in such a manner that generates mattes of these compositions. J.W. Matousek earned his Ph.D. in metallurgical engineering at Queens University. He is currently an independent consulting engineer. Dr. Matousek is also a member of TMS.     

Investigation of the effect of tooling parameters on weld formation in resistance flash welding

Special features of the process of resistance flash welding of ring-shaped components made of large-section pressed aluminium profiles are investigated. The effect of different parameters on the process of plastic deformation of metal during upsetting is studied. Recommendations are given for decreasing the number of defects in welded joints and increasing the wear resistance of the tooling.     

Impact of surface state in probeless friction stir spot welding of an Al–Li alloy

ABSTRACT

Sheets of AA2198 alloy with various surface conditions were welded with probeless friction stir spot welding (P-FSSW). Results show that the oxide layer on the original lap-weld surface produces continuously distributed oxide impurities at the interface of the P-FSSWed joint with a large amount of voids. The visual flow at the interface provides a persuasive explanation of local preferential abrasion. Following surface grinding, local abrasion increases with surface roughness and results in the dispersion of voids and oxides, which contributes to the improvement of metallurgical connection. The corresponding mechanical strength of the P-FSSWed joints shows a relatively significant increase, while the fracture mode remains affected by the hook defect regardless of the surface state.     

Estimation of mechanical properties of ferritic steel welds. Part 1: Yield and tensile strength

Abstract

The yield strength and ultimate tensile strength of ferritic steel weld metal have been expressed as functions of chemical composition, the heat input during welding, and the heat treatment given after welding is completed. The method involved a neural network analysis of a vast and fairly general database assembled from publications on weld metal properties. The outputs of the model have been assessed in a variety of ways, including specific studies of model predictions for the so called C–Mn and 2.25Cr–1Mo systems. Where possible, comparisons have also been made with corresponding methods which use simple physical metallurgical principles. The models created are believed to have been trained on the largest weld metal database to date, and are shown to capture vital metallurgical trends. The computer programs associated with the work have been made freely available on the World Wide Web.     

Improving the quality of layers deposited on rolling rolls by optimising the composition of flux-cored wires

ABSTRACT

Experiments were carried out to investigate the effect of adding carbon–fluorine compounds (the waste from metallurgical production) and nickel powder to the composition of flux-cored wires of the C–Si–Mn–Cr–W–V and C–Si–Mn–Cr–V–Mo alloying systems. The results show that the addition of these compounds to the composition of the charge for producing the wires of the 35V9Kh3SF and 25Kh5FMS types improves a large number of the characteristics of the deposited layer: reduces the extent of contamination with non-metallic inclusions, increases the hardness of the deposited layer, refines austenite grains and results in the formation of fine-dispersion carbides which in practice may improve the thermal resistance of rolling rolls, and also prevents the formation of a ferrite network which may have a beneficial effect on cracking resistance. The experimental results can be used to develop new compositions of flux-cored wires for hardfacing rolling rolls protected by Russian Federation patents. The hardfacing technologies of the rolls using these flux-cored wires with the C–Si–Mn–Cr–W and C–Si–Mn–Cr–V–Mo alloying systems are now produced by the ElSib company.     

Removal of Double Oxide Film Defects by Ceramic Foam Filters

In this study, Weibull statistical and statistical image analyses of porosity were employed to determine the efficiency of ceramic foam filters for the removal of double oxide film (bifilm) defects from a pure Al melt. Using these efficiencies and the branch filter model, the average size of the inclusions present in the liquid was estimated, and assuming that most of the inclusions in the melt are in the form of double oxide films, the possible dimensions for these defects were calculated. The results showed that the foam filters can remove oxide defects from the melt and that the efficiency of this filtration depends on the pore size of the filter. The average dimension of the oxide film defects was calculated to be 13.8?×?13.8???m with a maximum thickness of 1???m, if they remained non-convoluted in the metal flow. If they became convoluted because of the turbulence of the liquid flow, then the dimensions of the flat defect before it became curled up in the flow were calculated to be between 37?×?37?×?1 and 370?×?370?×?0.01???m.     

铱与镍基合金焊接接头的组织与性能分析

为解决原有火花塞中心电极焊接工艺造成的贵金属用量多、焊接不牢靠以及易产生裂纹、气孔等问题,通过电子探针(EPMA)研究了不同焊件结构对焊接区域的元素的扩散、材料之间的冶金结合的影响,通过扫描电镜(SEM)研究了不同结构对焊接区域断口界面组织的影响,同时测试了不同结构焊件样品的电阻率及弯折强度。结果表明,采用平面结构焊接,确保了焊接端面的接触,有利于材料的冶金结合,虽然弯折强度降低了11. 6%,但是整体焊接稳定性有所提升,同时大幅度降低了焊接气孔生成的几率,降低了平均电阻率,提高了整体性能。     

Shrinkage porosity in thin walled AM60 HPDC magnesium alloy U-shaped box

Abstract

The porosity distribution in AM60 High Pressure Die Cast (HPDC) boxes was studied. Boxes were either cast conventionally, or with liquid metal protection from oxidation by means of argon gas atmosphere in the sleeve. The inert atmosphere reduced the presence of oxide inclusions and porosity in the castings. Porosity was concentrated in continuous bands or clusters, depending on the distance from the gates. A high oxygen and aluminium segregation was revealed in association with bands of porosity. Porosity reduction and the absence of oxide films defects, both obtained by means of argon protection in the sleeve, produced an increase in the elongation to fracture which could be related to ductility and density.     

Bobbin tool friction stir welding: a review

ABSTRACT

Friction stir welding is a solid-state welding technique for joining similar and dissimilar material. Bobbin tool friction stir welding (BTFSW) is a variant of the conventional friction stir welding process (CFSW). Compared with conventional FSW, BTFSW eliminates all limitations of CFSW using a two shoulders configuration. Now, the need has arisen to review the work done on BTFSW to provide broader aspects of the technique to researchers. This paper aims at providing comprehensive insight on the BTFSW. The paper pays critical attention to tool material selection, design features of shoulder and pin surfaces, microstructure evolution, mechanical characterisation, derivatives, and challenges in this technique. Further, welding defects and future scope of BTFSW are also addressed in this paper.     

Effect of dissolved hydrogen on removal of double oxide film defects from Al melt

Abstract

Effect of increasing the hydrogen content of the melt on the removal of double oxide (bifilm) defects in commercial purity Al melt was investigated using Weibull statistical analysis of mechanical properties of solidified castings and a semiempirical mathematical model that had been developed previously. The results of the Weibull analysis revealed that increasing the H content of the melt from 0·2 to 0·4 mL/100 g and holding the melt in furnace for 30 min caused the Weibull modulus of the casting to increase by ～73%. Studies (SEM and EDX) of fracture surfaces of the test bars indicated that the number of oxide defects in the melt decreased due to this treatment. The mathematical model suggested that increasing the H content of the melt to ～0·8 mL/100 g would force all the oxide defects to expand rapidly and float out of the liquid metal in a very short time.     

Expert system shell for welding preheating: Technical and economic problems,as well as its impact on the physical environment (Part 2)

Summary

This article, published in three parts, is based on a doctoral thesis undertaken at the Department of Applied Mechanics and Engine Construction of Genoa University in collaboration with the Italian Institute of Welding. The aim of this article is to study the thermological, metallurgical, economic and safety problems of preheating which arise in fusion welding of steels and to acquire a basic knowledge of these phenomena as fully and logically as possible. On this basis, a simple, flexible and expandable tool, illustrated by experiments, has been devised for use by expert welding engineers.

For this purpose, state‐of‐the‐art research, national and international standards were studied and experimental tests conducted to correlate available data.

An expert system was thus produced, using artificial intelligence techniques, in order to determine preheating temperature, evaluate costs, and make health and safety recommendations to the user. This second section considers the issues of economics, safety and the environment.     

钢轨闪光焊接工艺与接头落锤试验分析

试验采用YHG-1200TH型移动式钢轨闪光焊机,焊接武钢60 kg/m U71Mn G热轧态钢轨.通过观察分析焊接曲线中闪平、脉动闪光、加速闪光与顶锻保压各阶段电流、电压、钢轨位移、压力等因素,结合接头落锤试验情况,调整并优选出合理工艺参数;分析焊接热输入与顶锻量间的搭配关系及接头抗落锤次数,观察断口与接头显微组织.结果表明,试验用钢轨闪光焊接热输入在11.5~12.5 MJ之间且顶锻量在15~16 mm之间时,接头抗落锤情况较集中,质量稳定性好;合理工艺参数焊接且经落锤检验合格的接头断口无明显缺陷,焊缝及热影响区组织为珠光体和少量铁素体,未见马氏体、贝氏体组织或其它缺陷.     

Investigation of weld defects in dissimilar friction stir welding of aluminium to brass by radiography

Abstract

The present study was focused on detecting weld defects in dissimilar joints made by friction stir welding. Radiography test and optical microscopy were used to evaluate the main defects. Coarse and continuous fragments of brass in aluminium matrix, tunnelling and void defects in vicinity of fragments were the main observed defects.     

Finite element modelling of resistance spot welding of aluminium with spherical tip electrodes

Abstract

A FEM based simulation model of the resistance spot welding process has been developed. The current simulation accounts for the non-uniform current density distribution in the sheet-electrode geometry and the elastoplastic deformation of the sheet due to electrode force, especially with spherical tip electrodes, since these effects are driven by and contribute to the main heat transfer analysis, which is governed by the internal heat generation within the sheet-electrode geometry as well as along the contact surfaces. The latent heat of transformation during melting or solidification, the variation of sheet/sheet contact resistance with temperature, and temperature dependent thermophysical material properties have been incorporated. The model also calculates the local time-temperature history of the sheet-electrode geometry that can be coupled with appropriate metallurgical reactions to determine metallurgical changes and subsequent mechanical properties in both the fusion zone and the HAZ.     

Production of new welding fluxes based on silicomanganese slag

ABSTRACT

The properties of a welding flux based on the silicomanganese slag are investigated. The flux is produced using the slag formed in the production of silicomanganese with different ratios of the slag fractions and different content of the water glass in the flux addition. The addition of up to 20–30% dust fraction of the silicomanganese slag to the composition of the flux results in excellent mechanical properties of specimens taken from the welded plates. The FD-UFS addition reduces the extent of contamination with non-metallic inclusions and reduces the size and amount of these inclusions. The optimum content of the water glass in the flux (up to 20–30%) was determined. Consequently, the resultant mechanical properties of the specimens taken from the welded plates are very high.     

Dihedral angles in Cu–1 wt.% Pb: Grain boundary energy and grain boundary triple line effects

The dihedral angle shown by intergranular lead inclusions in Cu–1 wt.% Pb alloys is measured varying the purity of the metal and the temperature. Several measurement methods are used and compared, namely classical two-dimensional (2D) methods based on metallurgical cross-section analysis and a recently developed 3D stereoscopic method that yields the true three-dimensional angle value for individual inclusions straddling a flat grain boundary. We confirm and extend earlier measurements using the new method. We show that a discrepancy found between the literature data and the stereoscopic 3D dihedral angle measurements is not caused by impurity effects. Rather, the data indicate that the discrepancy has its origin in a difference in average dihedral angle values measured between inclusions straddling two grains and values found at inclusions located where three or more grains meet.