Showing papers in "Materialwissenschaft Und Werkstofftechnik in 2019"

Shot peening using spherical micro specimens generated in high‐throughput processes

Abstract: Mechanical surface treatment processes like shot peening induce plastic deformation in the near surface areas of the peened workpiece leading to changes in surface and subsurface properties, e.g. hardness alteration and generation of compressive residual stress. While changes of the processed part are desired because of the lifetime extending influence, changes of the shot material are normally neglected as it is chosen to be highly resistant. Within this work plastic deformation of the shot material X210Cr12 and AlSi12 is examined. By investigating the plastic deformation of the particles, an indirect analysis of material properties, e.g. the yield stress or the hardness, is possible. A consideration of the particle velocities also enables conclusions about the materials properties. Those properties are conventionally obtained in a material, time, and cost intensive way. Using the same jet pressure, the investigations show lower velocities and less pronounced plastic deformation for the X210Cr12 specimens. Due to their higher mass, the X210Cr12 particles of same diameter are accelerated slower and therefore reach a lower impact velocity compared to AlSi12 particles. Furthermore, the lower plastic deformation at identical velocities can be explained with the higher yield stress of the X210Cr12 particles.

The influence of post‐heat treatments on the tensile strength and surface hardness of selectively laser‐melted AlSi10Mg

Abstract: To improve the mechanical properties of cast aluminium alloys several post‐heat treatments are known. However, these treatments cannot directly be transposed to additively via selective laser melting manufactured aluminium alloys, e. g., aluminium‐silicon‐magnesium (AlSi10Mg). Therefore, this study aims to determine suitable post‐heat treatments to optimise the mechanical properties of SLM‐built AlSi10Mg specimen. The influence of various post‐heat treatment conditions on the material characteristics was examined through hardness and tensile tests. The findings indicate that the Vickers hardness and ultimate tensile strength could not be improved via secondary precipitation hardening, whereas the fracture elongation shows a value which is distinctly higher than the values of a comparable cast alloy. Solution annealing at 525 °C reduces the hardness and the ultimate tensile strength by about 40 % and increases the fracture elongation three times. A subsequent precipitation hardening allows recovery of 80 % of the as‐built hardness, and 90 % of the previous ultimate tensile strength combined with maintaining an improved fracture elongation of about 35 % compared to the respective as‐fabricated condition.

Effect of amorphous silica by rice husk ash on physical properties and microstructures of recycled aluminium chip AA7075

Abstract: High strength to weight ratio of aluminium reinforced as metal matrix composites is a well known material used in automotive application. The effects of recycled aluminium chips AA7075 with amorphous silica by rice husk ash on the physical properties and microstructure were investigated. Recycled aluminium chip AA7075 was reinforced with agro waste of amorphous silica rice husk ash i. e., 2.5 %, 5 %, 7.5 %, 10 % and 12.5 %. Samples of these metal matrix composites were prepared by cold compaction method due to the lower energies consumption and operating cost compared to conventional recycling by casting. Physical testing of density, apparent porosity, water absorption and hardness tests of the metal matrix composites samples were examined in the current study. The density of metal matrix composites was increased up to 5 % of amorphous silica, and then decreased with increasing mass fraction of amorphous silica. Porosity and water absorption of metal matrix composites were significantly consistent at increasing mass fraction of amorphous silica, while the hardness of metal matrix composites was increased at increasing amorphous silica. Consequently, the microstructures of metal matrix composites were observed via optical microscope to analyze the dispersion of the reinforced composites. The microstructures of metal matrix composites were found non-homogeneous and random distribution of amorphous silica and aluminium chip AA7075 compared to 100 % recycled aluminium chip AA7075. Based on investigation to aluminium reinforced rice husk ash composites, it has good potential to improve the material behavior of metal matrix composites by appropriate composition amorphous silica to composite.

Influence of the jet velocity on the weld quality of magnetic pulse welded dissimilar sheet joints of aluminum and steel

Abstract: The object of this investigation is to determine the influence of the jet velocity on the weld quality of sheet joints produced via magnetic pulse welding. The use of a suitable high-speed camera system enables to observe the jet in detail, to determine its velocity during the collision process and to compare them to the achieved qualities (tensile strength, weld seam characteristics) of the welded samples. The results show that the quality of the weld generally correlates with the jet velocity, however the mere consideration of its velocity proves not to be a promising approach for predicting a specific weld quality. It becomes evident that the jet thickness has to be considered, since quality-critical characteristics of the weld seam appears in greater extent when the jet thickness increases.