In this study, the monotonic and cyclic material properties of steel material of medium static strength produced additively in the wire arc additive manufacturing (WAAM) process were investigated. This investigated material is expected to be particularly applicable to the field of mechanical engineering, for which practical applications of the WAAM process are still pending and for which hardly any characteristic values can be found in the literature so far. The focus of the investigation was, on the one hand, to determine how the material characteristics are influenced by the load direction in relation to the layered structure and, on the other hand, how they are affected by different interlayer temperatures. For this purpose, monotonic tensile tests were carried out at room temperature as well as at elevated temperatures, and the cyclic material properties were determined. In addition, the hardness of the material and the residual stresses induced during production were measured and compared. In addition to the provision of characteristic properties for the investigated material, it was aimed to determine the extent to which the interlayer temperature influences the strength characteristics, since this can have a considerable influence on the production times and, thus, the economic efficiency of the process.

During manufacturing of components using wire arc additive manufacturing, specific cooling times are required to prevent overheating of the structure and geometrical distortions. Currently, these cooling times are inserted based on experience at certain interlayer temperatures — which reduces the reproducibility, leads to unwanted component properties, and increases the process time. In this contribution, instationary thermal finite element simulations are applied to compute the temperature evolution of additively manufactured components using the inactive element method. This allows to optimize the process parameters, which are — in our considerations here — the welding velocity and the cooling time of each layer, to reduce the total process time while achieving sufficient component properties. The optimization is carried out with the gradient-free Nelder–Mead simplex algorithm, where certain constraints of the process parameters are considered via penalty functions. To obtain reasonable simulation results, the temperature-dependent heat transfer of the experimental setup is modeled and calibrated with experimental data beforehand. It becomes apparent that thermal finite element simulations combined with a gradient-free optimization procedure are a suitable numerical tool to perform the optimization of process parameters for wire arc additive manufacturing. The optimized process parameters fulfill certain requirements regarding the cooling of the manufactured component. Moreover, the optimized parameters can significantly reduce the process time compared to manually chosen parameters. In our example, this is around 48 %.

Due to the inherent properties of the process, arc-based generative manufacturing offers the possibility, of specifically applying different material properties locally. One possibility to realize this is the use of different materials. Three approaches are presented to illustrate this option. First, anisotropic behavior in the welding direction is generated. For this purpose, a FeNi36 is specifically combined with a low-alloy ultra-high-strength fine-grained structural steel filler metal. It will be shown that the integral component properties can be specifically adjusted in the welding direction. In addition, the metallurgical and welding characteristics will be discussed. As a second possibility, the use of well plasticizable materials to locally increase the material strength under cyclic loading with locally notched components is presented. For this purpose, an austenitic FeNi36 with good plasticizability and a good yield strength ratio for the application was applied to a fillet weld of a high-strength fine-grained structural steel in the weld seam toe. It is shown that the tolerable cyclic load can be improved by 35% by this procedure. Thirdly, it is shown that the required thickness of corrosion protection layers can be reduced by 50% through a targeted production sequence in arc-based generative manufacturing.

This paper shed light on the kinetics of transformation and the developed microstructure during wire arc additive manufacturing (WAAM). Three microalloyed alloys, two of them are high strength low alloyed steel (HSLA) grades and the third is a Ni-Cr-Mo steel, from which the welding wires are being produced, were investigated. Repeated cycles around varied temperatures from a reheating temperature of 1350 °C and down to a temperature 35 °C below the A_e1 are applied using dilatometer on samples from the steels. After applying the cycles, the dilatometric-samples were investigated metallographically and their macro- and microhardness values were measured. It is shown that the WAAM using HSLA steels produce softer structure than the steel of the welding wire. Combined microalloying with Ti and Nb can present a useful strategy for producing finer structure in the WAAM components due to the effect of Ti in inhibiting the prior austenite grain-growth and that of Nb in refining the final structure. Additionally, repeated heating near A_e3 refines the prior austenite grains and produced fine ferrite-pearlite structure in case of HSLA steels and a microstructure predominated by the granular bainite in case of welding wire alloy. The former microstructure was the softest one for the case of HSLA steels, whereas the softest structure in case of the welding wire alloy was the tempered martensite structure developed by reheating below A_e1. Idealized temperature curves were chosen for the heat treatment, which could be characterized in a well-defined manner. In future work such idealized curves together with temperature histories obtained in WAAM-process will be used to set up a database to train an AI-model for predicting structure and material properties.

The tracer diffusion of aluminium in the CuCr1Zr alloy was investigated, a material widely employed as an electrode in resistance spot welding. As a tracer layer, an alloy of Cu – 8.8 at.% Al was used, which was deposited by ion-beam sputtering. Isothermal diffusion annealing experiments were carried out between 500 and 700 °C, at temperatures relevant for industrial welding conditions. Al depth profile analysis was done by Secondary Ion Mass Spectrometry. The results revealed that aluminium exhibits a temperature-dependent diffusion behaviour. The diffusivities can be fitted together with literature data on Al diffusion in pure Cu obtained at higher temperatures according to the Arrhenius law. An activation enthalpy of 2 eV is obtained. The influence of a surficial oxide layer on the diffusion process is discussed.