Han Sur Bang

The Evaluation of Weldability for AZ31B-H24 and AZ91C-F Mg Alloys in Friction Stir Welding

In the present study, an investigation has been carried out on the friction stir welding (FSW) of two magnesium alloys. Hot-rolled and Die-casting plates of AZ type magnesium alloys were successfully joined by friction stir welding. AZ31B-H24 and AZ91C-F plates with the thickness of 4mm were used, and the microstructural development in stir zone (SZ) was investigated using optical and scanning electron microscopes. Hardness of SZ in AZ31B-H24 alloy has been slightly decreased due to the coarse structure. On the other hand, Hardness of SZ in AZ91C-F alloy has been remarkably increased due to very fine recrystallized grain structure. The result of EPMA showed Al Solid solution hardening by Solid solution of β intermetallic compound to α-Mg. While tensile strength of the FSWelded AZ31B-H24 alloy showed about 80% values compare to Base metal, AZ91C-F showed about 68% values due to strongly affected by formation of the intermetallic compounds, β-Al12Mg17.

Analysis of Complex Heat Flow Phenomena with Friction Stir Welding Using 3D-Analytical Model

Friction stir welding is being attracted and developed as an efficient joining method in the manufacturing field of Automobile, Aerospace and Ship building industries. As the FSW develops, more scientific research work investigations in this field have also been increased. Recent studies in FSW have revealed that both heat and metal flow characteristics have a non-symmetric complex nature about the tool axis. But until now there is no efficient 3D- heat flow model to be comparable with the experimentally measured values. The body of the work covered FSW of Al6061 and its thermal distribution based on a nonsymmetrical analytical model for the heat input in to the matrix of Al plates from FSW tool due to the effect of combined translation and rotational motion of the tool pin and shoulder. Finally the 3D- finite element heat transfer analysis program has been used to plot the heat distribution at the Friction Stir Welded joint in Al 6061 plate. The work concludes that the heat distribution result obtained from FE analysis has a reasonable agreement with the experimentally measured values.

Laser Weldability of Aluminum Alloy and Steel

With the intention of improving butt or lap joint of dissimilar materials, specially devised weld beads together with lap and butt-joints were produced between A5052 and SPCC, where A5052 butt-joint was melted by heat-conduction of SPCC weld bead in addition to the formation of a limited weld fusion zone at the lap part in A5052 alloy. The thickness of intermetallic compounds at the butt-joint interface was approximately 2 μm and free of cracks. It was also revealed that crack-free lap weld metals were formed between aluminum alloy and steel when the penetration was controlled to be of less than 0.3 mm in depth at small heat input. It was moreover found that the majority of a laser weld fusion zone solidified as alpha(bcc)-iron phase containing small amount of aluminum, and cracks were absent in the case of hard intermetallic (AlxFey type) layer of less than 10μm zone. It was confirmed that a weld with lap and butt joints possessed high strength (leading to the load 3500 N to 4,380 N for 40 mm width specimen). In addition, SPCC and A1100 or A5052 were subjected to lap welding with a cw YAG laser, where one to three passes were performed to produce wider bonded areas. Dissimilar steel and aluminum joints with good mechanical properties were obtained, since the fracture occurred in the aluminum alloy base metal in the tensile test. It is concluded that welded joints of high strength can be produced between aluminum alloy and steel with proper devices.

Effect of Strength Mismatch on Ductile Crack Initiation Behavior from Notch Root under Static Loading

It has been well known that ductile fractures of steels are accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameter criterion based on equivalent plastic strain and stress triaxiality. It has been demonstrated by authors using round-bar specimens with circumferential notch in single tension that the critical strain to initiate ductile crack from specimen center depends considerably on stress triaxiality, but surface cracking of notch root is in accordance with constant strain condition. This study fundamentally clarifies the effect of strength mismatch, which can elevate plastic constraint due to heterogeneous plastic straining under static loading, on critical conditions for ductile cracking from the pre-notch root. In order to evaluate the stress/strain state in the pre-notch root of specimens, a thermal elastic-plastic finite element (FE) analysis has been carried out.

Welding of Steel and Aluminum by Nd-YAG Laser

In this present study, the author used continuous YAG laser to weld the lap joint of steel and aluminum plate. Specimens used are SPCC, A1100 and A5052 and laser beam is radiated on the upper side of steel plate so that laser is absorbed higher by steel than aluminum. Lap joint weldments are produced by changing the welding speed, keeping all other welding parameters same. After welding, fracture path, crack tendency, penetration and thickness of intermetallic layer were investigated by tensile test, Scanning Electron Microscopy and Energy Dispersive X-ray Spectrometer. From the test results it is revealed that crack free weldment are produced successfully and penetration depth of lap joint should be controlled to minimize thickness of intermetallic layer thus to get higher joining strength. Introduction Welding or joining of dissimilar material is difficult and have limitations because physical properties of each material like melting temperature, heat expansion coefficient, conductivity, yielding point, etc. are different. Despite difficulty in joining dissimilar material, more efforts and researches are concentrated on the field of dissimilar joining in near future due to many technical and economical advantages. Present paper include the experimental results of dissimilar material welding using continuous YAG laser beam on lap welded joint of steel and aluminum. Compare with conventional fusion welding process, high density energy beam such as laser can be used more superiorly on dissimilar material welding due to high welding efficiency and narrowly focused fusion zone. In all types of welding methods, intermetallic compounds are produced inevitably by welding and joint strength is influenced by the amount of intermetallic compounds. Generally, this intermetallic compounds formed in welded interface are very brittle and hard therefore effect badly on strength of welded joint thus the effort to reduce the amount of intermetallic compound is necessary to get higher joint performance. When we weld dissimilar material by laser beam, controlling the heat input, it is more flexible than fusion welding and by applying appropriate heat input condition we can make a weld with less intermetallic compound and can make strength of welded joint higher. Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 2389-0 doi:10.4028/www.scientific.net/KEM.270-273.2389

Fracture Study of Ultrasonic Aluminum Wire Wedge Bonding on Copper Substrate with Mechanical Peeling-Off Method

In this paper, the characteristics of bond interface and bonding mechanism were investigated with peeling-off method. The fracture was observed and interfacial composition was certified by map scanning of EDX (Energy dispersive X-ray analysis). Based on the features of interfacial characters, the actual joining area mainly distributed at bond periphery; non-bonded at bond center. When the bonding time was lower, the ratio of the bond length to its width was larger and elemental aluminum distributed discontinuously on the bond fracture, primarily at the periphery. After aging, the fractures were also analyzed and Cu2Al3 intermetallic compound (IMC) was identified. The phenomena of bond interfacial tracings were analyzed, and the bonding mechanism was ascribed to plastic flow analyzed by finite element method based on the contact issues.

Numerical Simulation of Al-SPCC Weldment

Analytic procedure for dissimilar materials welding problem by using developed in-house solver is applied on butt and lap jointed model. In addition, the procedure of data transferring between commercial package and in-house solver for the preparation of input data for in-house solver has been developed. Therefore we can use the commercial package as pre and post processor for in-house solver and the results from in-house solver, for example, welding residual stress can be exported to commercial package as initial value to the model and then further analysis with the application of external loading can be carried out. For the similar material welding the welding residual stress has been decided by temperature dependent material properties that are input to the source program. In the case of dissimilar welding problem due to the difference of expansion and shrinkage rate between aluminum and steel there has been a slight variation in this dependency. Since the aluminum has large thermal expansion coefficient and the mechanical melting point is lower than steel, the order and level of mechanical behavior like stress history become different. The degree of mechanical deterioration of dissimilar materials welded model has been assessed with various view aspects, namely, welding residual stress, plastic strain, equivalent plastic strain and plastic work distribution and it has been revealed that Al5052 is mechanically more sever than SPCC for same heat input.

A Study on the Lamination Produced by Corner Joint Welding of Ultra Thick Plate by Newly Designed Z-Quality Evaluation Methods

In welding for the corner joint of box-column structure with a ultra thick plate of 80mm, lamination occasionally occurs along the mid-thickness of the flange plate. In attempts to evaluate z-quality of ultra thick plates in a reliable and quantitative manner, newly developed destructive and non-destructive tests were applied to steels with different Z–quality. A wide-plate tensile test for z-direction sample was firstly suggested, and the test, compared with the conventional z-direction tensile test by a small tensile specimen, could be used to evaluate the different z-quality quantitatively. To evaluate z-quality of ultra thick plates with different degree of segregation in a non-destructive way, an electrical resistivity was measured for steels with different degree of segregation, and it showed discretely different electrical resistivity. The higher segregation a steel had, the higher electrical resistivity it showed. F.E.M. analysis foptimum groove design and welding procedurehe full penetration condition of Model 3 seemed good for preventing welding residual stress and strain because the anticipated crack point was restrained by the deposited weld metal. Introduction With increasing application of large scale steel structures to buildings, bridges, ships, and offshore structures, the use of ultra-thick plate box columns has increased and this trend is expected to be continued[1]. In producing ultra-thick plates by continuous casting and hot rolling process, a segregation band of solute atoms, such as carbon, manganese, phosphorous and sulphur, can form along the center layer of the plates. This linear band leads to discontinuities in chemistry, resulting in inhomogeneous microstructure and properties through the plate thickness direction. During welding of such plates for high restraint structures, an internal crack, known as lamination, occasionally occurs along the linear discontinuous layer in the mid-thickness of the plate, owing to the combined effects of ductility loss in that reason and applied external force[2]. Lamination along the mid-thickness segregation band has been revealed to be associated with metallurgical factors inherited from the segregation band, and welding residual stress acting on the plates along the through thickness direction. The metallurgical factors associated with this defect are elongated non-metallic inclusions, hardened and less ductile phases, and hydrogen, that is, the defect has been known to be caused by elongated manganes sulfides along the centerline segregation band, and the presence of a large volume fraction of hardened phase such as martensite-austenite constituents and diffusible hydrogen absorbed from the weld metal. To reduce the occurrence of the defect, steel manufacturers attempt to eliminate segregation of solute atoms during continuous casting process, and fabricators consider the optimum groove design and welding conditions to reduce the welding residual stress and restraint stress[3-4]. In the present study, in attempts to evaluate z-quality of ultra thick plates in a reliable quantitative manner, newly developed destructive and non-destructive tests were applied to steels with different z–quality. An F.E.M. analysis was also carried out for the welding residual stress and residual strain using heat conduction, heat transfer, and heat elastic-plastic analysis studies pertaining to the welding strength, by changing the penetration condition, groove shape, and welding procedures. An attempt was then made to optimize welding conditions for the reduction of lamination. Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 2377-2382 doi:10.4028/www.scientific.net/KEM.270-273.2377