Investıgatıon of Cold Weldıng At Steel-Alumınum Combınatıons Vıa Extrusıon Process Usıng Thermo-Mechanıcally Coupled Fınıte Element Analysıs

Abstract

In this century, the importance of weight reduction studies has been increasing day by day, and the importance of hybrid structures have also increased. Especially, reducing the weight in aviation and automotive industries, emission rates can be reduced, costs can be reduced and also, more sustainable structure are created. Accordingly, cold welding method applied in extrusion process is an effective method to form hybrid structures. Although the cold welding process starts at room temperature, it reaches up to185 C values formed between the parts. When the literature is examined we see that, the effect of treatment, surface enlargement and contact normal stresses between the materials were investigated by experimental and finite element method. However, these studies were done either mechanically or thermally. In this study, the contact normal stresses between the materials, surface enlargement values and temperature effect of material flow were examined by thermo-mechanical finite element analysis. Actually parameter effecting cold welding is investigated by thermo-mechanical finite element analysis. For this purpose, the properties of EN AW-6082 T6 and C10 (1.0301) plain carbon steel materials were tested by compression test and the parameters of Johnson-Cook material model were obtained and these parameters were implemented in a finite element model. The shape of the sample is cylindrical. The core of the cylindrical part is made of aluminum and the outer part is made of steel. The outer diameter of the used steel material is 15 mm. Diameters of aluminum materials are 6.5 mm, 7.5 mm and 8.5 mm. Cylinder materials were extruded to 11.1 mm and 9.6 mm, corresponding to 0.6 and 0.9 strain values, respectively. In addition, the materials were extruded at 30 °, 45 ° and 60 ° die angles. In this study, different plastic strain values, different die opening angle values, surface enlargement and contact normal stresses formed between the aluminum and steel parts were investigated thermo-mechanically by using finite element analysis. When the results are investigated, temperature of the materials are higher at high strain. In addition, maximum temperature is seen at exit of the deformation zone. When die angles are examined, on the aluminum part there is no significant effect but there is a significant effect on the steel part. Temperature of steel part increases by increasing die angle. Furthermore, there is any effect on material temperature when the heat treatment effect is investigated. Contact normal stress is an another factor effects of success of cold welding. It is generally expected that contact normal stress is 2 times yield of material. Contact normal stresses decrease by increasing die angle. Conversely, contact normal stresses is higher at high strain. Finally, when the surface enlargement is examined materials, diameters of materials does not affect surface enlargement and surface enlargement is higher on aluminum part than steel. Besides surface enlargement is higher at high strain value.