Welding Metallurgy of

Prospects of laser beam welding and friction stir welding processes for aluminum airframe structural applications

Friction Stir Welding(摩擦撹拌接合)法の熱工学的研究

Joining aluminum to steel can lighten the weight of components in the automobile and other industries, which can reduce fuel consumption and harmful gas emissions to protect the environment. However, the differences of thermal, physical, and chemical properties between aluminum and steel bring a series of problems in laser welding. The main problems are how to control the thickness of the intermetallic compound layer and reduce or avoid the generation of pores, cracks, and thermal stresses which severely limit the mechanical properties of welded joints. Laser fusion-brazing technology utilizes the precise control of heat input with or without filler to partially melt the low melting temperature aluminum base material and promote wetting on the high melting temperature steel base material in order to achieve sound metallurgical by combining the advantages of fusion welding and brazing. Different forms of laser beam welding including single beam laser welding, dual-beam laser welding, and laser arc hybrid fusion-brazing welding are reviewed.

Laser welding dissimilar materials of aluminum to steel: an overview

The present paper is focused on friction stir welding (FSW) of dissimilar aluminum alloys and steels, an area that is getting great concern recently The promise of FSW joints lies in low welding heat input and its ability to minimize the extent of the formation of intermetallic compound (IMC) in dissimilar metals The present paper assessed the status of FSW process of dissimilar aluminum alloys and steels, and to identify the opportunities and challenges for the future The essential reason for the formation of the dissimilar Al/steel FSW joints with high quality is explained by super diffusion behavior This paper will provide basis to designers and engineers to consider FSW for a wider range of dissimilar aluminum alloys and steels

Friction stir welding of dissimilar aluminum alloys and steels: a review

In this study, effects of different operating conditions on friction stir welding (FSW) of dissimilar sheets of 5050 aluminum (Al) alloy and 304 stainless steel have been investigated. Recently, FSW process has been used for joining of dissimilar materials due to its ability to eliminate local casting defects of the conventional fusion welding techniques. Microstructure and mechanical properties of weld nugget in FSW process mainly depend on several parameters such as tool rotational speed, feed rate, offset, and pin profile. In the present work, effects of tool rotational speed, feed rate and offset, together with annealing process on the tensile behavior and microhardness of the welding procedure were investigated and discussed. Based on the experiments, our results showed that decreasing tool rotational speed from 710 to 500 rpm besides increasing tool feed rate from 40 to 80 mm/min leads to an improved joint. Furthermore, the defect on the stirred zone was decreased by increasing the tool offset up to 1.5 mm. On the other hand, enhancements of up to 100 and 9 % in elongation and tensile strength were achieved by applying the annealing process, respectively.

Microstructural and mechanical properties of friction stir welded 5050 Al alloy and 304 stainless steel plates

Forming conical parts is one of the complex and difficult fields in sheet-metal forming processes. Because of low-contact area of the sheet with punch tip in the initial stages of forming, bursting occurs on the sheet. Moreover, since most of the sheet surface in the area between the punch tip and blank holder is free, wrinkles appear on the wall of the drawing part. Thus, these parts are normally formed in industry by spinning, explosive forming, or multi-stage deep drawing processes. In this paper, forming pure copper and St14 conical–cylindrical cups in the hydrodynamic deep drawing process was studied using finite element (FE) simulation and experiment. The effect of pressure path on the occurrence of defects and thickness distribution and drawing ratio of the sheet was studied. It was concluded that at low pressures, bursting occurs on the contact area of sheet with punch tip. At higher pressures, the cup was formed, but the wall thickness distribution depends on the pressure path. It was also illustrated that for the pressure path with a certain maximum amount, the workpiece was formed adequately with minimum sheet thickness reduction. Internal pressures more than this maximum amounts did not affect on the thickness distribution. By applying the desired pressure path, conical–cylindrical cups with high deep drawing ratio were achieved.

Investigation of hydrodynamic deep drawing for conical–cylindrical cups

In this paper, the effect of the main process parameters of high-velocity oxygen fuel (HVOF) thermal spraying on the particles characteristics and surface residual stresses of WC–12Co coatings was studied. Taguchi approach was used for design of experiments. Four more effective parameters such as spray distance, oxygen-to-fuel (O/F) ratio, powder feed rate, and gun travel speed were selected as inputs. The sin2ψ method was used to evaluate the surface residual stress by means of X-ray diffraction (XRD) method. Spray Watch diagnostic system, scanning electron microscopy (SEM), and XRD were used for this purpose. The statistical results showed that the spray distance and O/F ratio are the most effective factors on the particle characteristics and residual stresses. The particles velocity and temperature were varied in range of 418.8–449.4 m/s and 1749.2–2055.4°C, respectively. The surface residual stress was in the range of 31.9–84.6 MPa.

Parametric Study of Residual Stresses in HVOF Thermally Sprayed WC–12Co Coatings

The scope of this investigation is to evaluate the effect of welding parameters on the mechanical properties and microstructural features of 3-mm-thick AA7075-T6 aluminum alloy subjected to gas heating system as a preheating source during friction stir welding. Toward this end, a gas heating system was designed to heat up the weld seam just ahead of rotating tool to soften the material before being stirred. Three welding parameters, five levels, and a central composite design (CCD) have been used to minimize the number of experimental conditions. The joining parameters such as tool rotational speed, welding speed, and shoulder diameter have a significant influence on determining the mechanical properties of the welded joints. It was found that using preheating system mostly can result in higher total heat input into the weld joint and effectively reduces the formation of defects when unsuitable process parameters were used. Also, an attempt has been made to establish the mathematical model to predict the tensile strength and microhardness of the joints. The optimal welding conditions to maximize the final responses were investigated and reported. The results show that the joint fabricated at a rotational speed of 1,050 rpm, welding speed of 100 mm/min, and shoulder diameter of 14 mm exhibited higher mechanical properties compared to other joints.

Salman Nourouzi

Papers

Microstructural and mechanical properties of friction stir welded 5050 Al alloy and 304 stainless steel plates

Investigation of hydrodynamic deep drawing for conical–cylindrical cups

Parametric Study of Residual Stresses in HVOF Thermally Sprayed WC–12Co Coatings

Predictions of the optimized friction stir welding process parameters for joining AA7075-T6 aluminum alloy using preheating system

Effect of ECAP on microstructure and tensile properties of A390 aluminum alloy