Properties Evaluation of the Welded Joints Made by Disk Laser

The process of laser welding of sheets of HSLA (high-strength low-alloy steel), DP600 (dual-phase steel) and TRIP steels was investigated. A weld was successfully made in a double-sided hot-dip galvanized sheet with a thickness of 0.78–0.81 mm using a laser power of 2 kW per pass without any pretreatment of the weld zone. Microstructure studies revealed the presence of martensitic and ferritic phases in the weld zone, which could be associated with a high rate of its cooling. This made it possible to obtain good strength of the weld, while maintaining sufficient ductility. A relationship between the microstructural features and mechanical properties of welds made in the investigated steels has been established. The highest hardness was found in the alloying region of steels due to the formation of martensite. The hardness test results showed a very narrow soft zone in the heat affected zone (HAZ) adjacent to the weld interface, which does not affect the tensile strength of the weld. The ultimate tensile strength of welds for HSLA steel was 340–450 MPa, for DP600 steel: 580–670 MPa, for TRIP steel: ~700 MPa, respectively, exceeding the strength of base steels.

Material Model for the Production of Steel Fibers by Notch Rolling and Fulling

Concrete, which is reinforced by steel fibers, represents a multifunctional building material that is able to realize flexible but stable structures. As an alternative to the energy-intensive conventional production procedure wire drawing, a combination of a notch rolling and cyclic bending process is proposed by Stahl [1] to produce those fibers. Besides representing the properties of steel fibers and the overall process, the paper brings the layout of both process steps into focus. Since notch rolling for the production of wire strip is mainly unexplored, a general conceptual design of the process and the rolling tools is performed, supplemented by a similar study on the fulling process. To enable a further evaluation of the process chain and its relevant process parameters, a numerical and experimental test phase using strip of a dual phase steel DP600 with a sheet thickness of t0 = 0.8 mm is intended in future. For ensuring high-quality numerical model, relevant behavior of the test strip is characterized through appropriate experiments and according material models in the present paper.

Investigation of Different Joining by Forming Strategies when Connecting Different Metals without Auxiliary Elements

Lightweight constructions become more and more important, especially in the mobility sector. In this industry, the increasingly strict regulations regarding the emissions of carbon dioxide can be achieved to a certain extent by reducing the vehicle weight. Thus, multi-material systems are used. Conventional joining techniques reach their limits when joining different materials due to different thermal expansion, unequal stiffness or chemical incompatibilities. This is why additional joining elements or adhesives are used. These must be viewed critically regarding a lightweight and resource-efficient production, since they add weight or complicate the recycling process of these components. Consequently, there is a great and growing need for new versatile joining technologies in order to overcome these challenges and to be able to react to changing process parameters and boundary conditions. Joining without an auxiliary element using pin structures formed directly from the sheet metal plane is one approach to meet these challenges. These pin structures are then joined by direct pressing into the joining partner. This is possible with a variety of material combinations, but is advantageous with regard to continuous fibre-reinforced thermoplastic composites (CFRTP), as the fibres do not have to be cut when joining CFRTP using pin structures. In this paper, the formability of pin structures made of a dual-phase steel DP600 (HCT590X + Z) is investigated. The extruded pin structures are joined by direct pin pressing with an EN AW-6014 to form tensile shear specimens. Different joining strategies are investigated to compare their influence on the joint strength. The results have shown that it is feasible to form suitable pins from a DP600 dual-phase steel to produce reliable connections with an aluminium sheet joined by direct pin pressing.