As a result of studying the research trends of dissimilar metal joining using the arc heat source, the process parameters that determine the quality of the joints can be classified into the filler metal, type of coating, heat input energy and joint conditions such as the gap. Among these parameters, the joining mechanism has already been identified by many researchers from the metallurgical point of view such as the kind of the filler and the characteristics according to the heat input. Therefore, in this study, we tried to understand the joining mechanism related to kind of coating and wettability through high speed camera observation. We also studied the effect of not only the various coating but also the thickness of coating layer. As a result, there was a large difference in bonding property depend on the type of coating in the joint. In case of galva-annealed steel, the coating layer was not sufficiently melted due to a higher melting point compare with galvanized steel, so that a large amount of spatter was generated and no wetting occurred under any conditions. Also we cannot found the relationship between the thickness of the coating layer and the generation of the intermetallic compound. However, the difference about the quality of the joints is evident because the amount of Zn vaporized under the same heat input condition is increased.
In order to commercialize the steel to aluminum joining technology using arc heat source in the automobile industry, it is the most important to secure a reliable joining strength. However, there is not enough to describe the overall static strength characteristics of dissimilar metal joints. Therefore, in this study, the tensile-shear test was performed according to the process parameters which affect the strength of the lap joint structure. As a result, the porosity of the Al-Fe dissimilar joint has a greater influence on the strength due to the vaporization of Zn present in the root zone than the geometrical shape of the bonded length or the wetting angle. In addition, it was confirmed that the crack was initiated due to the root pore, along with cracks in the vicinity of the continuous pore by fractography analysis. Decrease of the tensile strength is due to the reduction of the absolute cross-sectional area result from the pores present in the weld metal. Finally, from the results of stress analysis using FEM, it was confirmed that the pore of the root zone due to the increase of the heat input had a greater influence on the strength even though the interface bonding length was increased.
Recently, various joining processes have been researched by many researchers due to the demand for the joining technology between steel and aluminum. Therefore this study is about the dissimilar metal joining of aluminum to steel by using the arc welding process which is used in the field the highest applicability. First of all, in this paper the research trends of each process applicable to the joining of steel and aluminum were investigated. Also we tried to confirm the characteristics through direct process comparison. As a result, the processes that can be applied to the joining of steel and aluminum can be classified into mechanical, chemical and thermal methods. However, until now, only the conventional method such as riveting and the structural adhesive is used for the joining of the two materials. In case of arc welding, although there are some restrictions due to Zn coating, relatively stable joints can be obtained in comparison with other welding processes. Therefore, it is considered that there will be sufficient competitiveness if a strong restraint against porosity is provided.
In order to commercialize the Fe-Al joining technology using arc heat source, it is necessary to guarantee about static and dynamic strength. However, no studies have been conducted to evaluate the fatigue strength of Al-Fe joints using arc heat sources. Therefore, ultrasonic fatigue test to the overlap joint structure of dissimilar materials was examined at first. For the ultrasonic elastic resonance experiment, the plate type specimen of the overlap joint was designed based on the design theory of the ultrasonic fatigue specimen. As a result, it was confirmed that the ultrasonic fatigue test for the overlap joint was sufficiently applicable through the thermal imaging camera measurement. Also the result of ultrasonic fatigue test according to the heat input and the presence of gap, the fatigue life depend on increasing heat input was reduced due to inverse proportion to the growth of the root pore. On the other hand, if the gap is present, fatigue life is improved up to 25% as much as the static strength by removing a considerable amount of pores. When compared to other studies on the fatigue of aluminum lap joints, this fatigue limit is sufficiently competitive if a method to control the pores is constructed.
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