Branislav Vanko

This study evaluates the applicability of lead-free SnAg5 solder in Resistance Element Soldering (RES) technology for joining an AISI 304 stainless steel sheet and a PMMA (polymethyl methacrylate) thermoplastic. The microstructure and properties of the resulting soldered joints were assessed. By utilizing Chemet CHM-A-014 flux, excellent wettability of the SnAg5 solder on the AISI 304 steel sheet surface was observed at 275 °C, achieving a contact angle of 3.5°. During resistance heating with the selected parameters, only a specific volume of solder in the core of the Cu/SnAg5 bimetallic elements was consistently remelted. Mechanical testing of the RES joints revealed that shear strength ranged from 26.66 to 39.32 MPa, which corresponds to 62–92% of the solder’s bulk shear strength. Joint failure occurred predominantly within the solder and partially at the steel/solder interface, with the fracture surfaces exhibiting a ductile character. Finally, XRD analysis confirmed that the dominant fracture path propagated through the solder, identifying the presence of FeSn₂ and Fe₂Sn intermetallic phases on the fracture surfaces.

This study investigated the microstructure and properties of soldered joints of AISI 304 stainless steel and PMMA thermoplastic or AW-1050A aluminum alloys made using Resistance Element Soldering (RES) technology. The bimetallic element used in RES provided a mechanical joint with a thermoplastic or aluminum alloy and a soldered joint with AISI 304 steel using Sn60Pb40 solder in the core of the element. The solder in combination with the Chemet CHM-A-014 flux wetted the AISI 304 steel surface very well at a temperature of 225 °C with a contact angle of 14°. During the production of the joints, the solder melted in the bimetallic element on the AISI 304 steel side, while solid solder was retained at the point of contact with the welding electrode. The strength of the joints ranged from 25.5 to 36.4 MPa, which was less than the strength of the solder, and the joints failed at the AISI 304 steel–Sn60Pb40 solder interface. The fracture surface was predominantly formed by the solder. An intermetallic phase of FeSn₂ was identified at the interface.

Resistance Element Soldering (RES) is one of the new methods of joining dissimilar materials by resistance heating using an element. Sn60Pb40 solder, which has been used for decades in tin smithing and the electrical industry, has already been tested for joining galvanized steel sheet with thermoplastic using RES. However, legal restrictions are currently moving towards prohibiting the use of lead in mass production. For this reason, the possibility of replacing Sn60Pb40 solder with Sn91Zn9 lead-free solder was verified. The results showed that with an appropriate choice of flux and resistance heating conditions, it is possible to replace Sn60Pb40 solder with Sn91Zn9 solder when joining galvanized steel sheet with thermoplastic using RES. With a suitable heat input during soldering, good conditions were achieved for wetting the base material with molten solder with a sufficient volume of remelted solder in the core of the Cu/Sn91Zn9 bimetallic element. The strength of the soldered joint made at a heat input of 901 J was measured at the level of 94% of the strength of Sn91Zn9 solder.

The work was focused on evaluating the influence of the structure of the protective Zn coating on steel sheets on arc welding. Two types of galvanized steel sheets were used in the experiments, HX340LAD + ZF (GA type) and HX300LAD + Z (GI type), with a thickness of 2 mm. First, the analysis of the structure of the Zn protective layer was carried out on the selected materials. After that, test welds were made using the gas metal arc (GMA) welding in the short-circuit metal transfer. The influence of the type of protective Zn coating on the occurrence of defects, the geometry of the weld, and the stability of the welding process was evaluated. From the achieved results, it can be concluded that the protective Zn layer on the HX340LAD + ZF sheet was formed by intermetallic phases Fe_xZn_y-Fe concentration ranged from 19.0 wt.% (at the steel plate coating interface) up to 9.5 wt.% (on the coating surface). An Fe-Al inhibitor layer was observed at the steel sheet-coating interface of the HX300LAD + Z material, while the Fe content in the Zn coating decreased from 8.2 to 0.8 wt.% towards the surface. Better weld evaluation results were achieved on samples made on HX340LAD + ZF galvanized sheet. The welds were without porosity, and the stability parameter (electric arc stability criterion) was almost two times smaller than the stability parameter in the evaluation of the HX300LAD + Z sheet metal welding process.

The contribution is devoted to the making of bimetallic semi-finished products for the production of elements, which are used to joining dissimilar materials, metal sheets to plastics, using the Resistance Element Soldering. During the making of bimetallic semi-finished products by gravity casting, defects occurred and, moreover, the proposed method of casting was not very productive. Therefore, centrifugal casting of bimetallic semi-finished products was proposed, which enables the production of a larger number of semi-products with higher quality in one casting cycle. The method was verified by preparing bimetallic semi-finished products Cu-Sn91Zn9 and Cu-Sn60Pb40. The non-destructive X-ray test proved the reliability of the centrifugal casting in the serial production of high quality bimetallic semi-finished products.

This work presents a new technology for joining dissimilar materials, Resistance Element Soldering (RES). This technology is fundamentally based on Resistance Element Welding (REW) technology; the difference is that the presented RES uses a bimetallic element composed of a hard Cu shell and a core made of Sn60Pb40 solder. The RES technology using the Cu/Sn60Pb40 bimetallic element was tested when joining a galvanized steel sheet (HX220BD-100MBO) to a thermoplastic (PMMA). The effect of the process parameters on the volume of the melted solder, the deformation of the element, and the structure of the soldered joint was investigated on the joints made. The final criterion for assessing the influence of the process parameters was the joint strength. Due to the low strength of PPMA, the maximum joint strength was determined on RES joints of galvanized steel sheet and aluminum. The results showed that, to ensure the joint strength at the level of the strength of the Sn60Pb40 solder used, a heat input of 952 J and a clamping force of 623 N are required. The mentioned parameters ensure the necessary conditions for the creation of a soldered joint with a galvanized steel sheet as well as the deformation of the bimetallic element to create a form-fit effect in the opening of the PMMA to create a mechanical connection.

The joining of sheet metal parts produced in the material combination of Fe-Fe, Fe-Al as well as Fe-thermoplastic and Al-thermoplastic can be realized by the Resistance Element Soldering (RES). Extruded bimetallic elements were used to form the overlap joint. The semi-finished product for extrusions was a Cu 99.9 tube with dimensions φ6 × 0.5 mm and length 9 mm, filled with Sn60Pb40 solder. “T” shaped overprints were produced in two ways. Simulation in the ANSYS software environment was chosen to optimize, select the appropriate forming process, and design the geometry of the functional parts of the forming tool, allowing to use only one extrusion forming operation. The results of the simulations are the magnitudes of stresses and strains, and different head shape geometries of the bimetallic element extrusions of the three proposed forming methods. The task was to achieve extrusions without defects of the Cu tube shell, such as corrugations and wrinkles. The geometry was observed and compared by macroanalysis of extrusion sections made on a laboratory forming tool.

The process parameters of the Laser Metal Deposition technology in the production of simple components made of NiCuBSi type metal powder were verified in this paper. A laser head with a coaxial powder supply and argon gas was used in the production. The powder was welded to a S235J2G3 steel plate. The used parameters (heat input 0.25 kJ.mm⁻¹) enabled the production of samples with a minimum porosity (1.2 %) and without the defects (cold joints, pores) between the weld layers.

The bimetallic joining elements were designed for lap joints of thin metallic (Fe-Fe, Fe-Al) as well as metallic – nonmetallic (Fe-PMMA, Al-PMMA) sheets by Resistance Element Welding (REW). The Cu tubes with an outer diameter of 4 mm, wall thickness of 0.5 mm, and a length of 11 mm filled with a solder Sn60Pb40 were used for the bimetallic joining elements producing. The required shape of joining elements is obtained by cold forming. Simulation by ANSYS software was chosen for the optimization of the forming process and geometry of functional parts of the forming tool allowing to use only one extrusion forming operation. The simulation results are stresses, strains, and modification of cross-section geometry of elements for the three proposed forming modes. The geometry of functional parts of the forming tool was compared with the results of cross-section macroanalysis of joining elements.