No abstract

Among various methods of material preparation before thixoforming, applied to obtain globular microstructure, like cold or hot deformation, Equal Channel Angular Pressing ECAP allows to obtain the correct microstructure after heating to the semi-solid range. In the present study 7075 aluminium alloy was cold pressed using ECAP method in order to obtain the appropriate semi-solid range microstructure. The bar of 7075 alloy annealed at 400 o C of diameter of 30 mm, was cold pressed using ECAP at a pressure of 800 MPa. Samples had only a small cracks and the hardness of 95 HV5. The characteristic temperature of the thixo-process was determined using DSC at 615 o C which is slightly higher than that used in the literature. A series of a gear shape samples were thixo-formed from the alloy after ECAP using modified high pressure die casting. The globular microstructure with the globule's size between 60µm -90m was observed. The hardness was lower than after ECAP, close to 80 HV5. Additionally, T6 heat treatment was performed: supersaturation from 460ºC and ageing for the period of 12 hours at 120ºC. Transmission Electron Microscopy TEM enabled identification of ' precipitates of size near 20 nm present in the alloy after the thixoforming and T6 treatment, responsible for a rise of hardness up to 150 HV5.

The use of additive manufacturing methods for the production of sand cores with organic binders is currently the latest trend in small and unit production, as it allows for a quick and simple way to get a final cast part; this is known as Rapid Prototyping. In this article, manufactured additive method cores were analyzed that were made of quartz sand with furfuryl resin and cores made of synthetic sand. Derivatographic measurements were compared, and examples of the high complexity cores are shown. Furthermore, the aspect ratio of the grains was determined by microscopic observation. Each type of core was characterized by a different flexural strength and differentiated results of abrasion. The results were collected and compared.

This article discusses the nucleation and propagation of microcracks in gravity-cast aluminum-silicon and aluminum-lit alloys. Microstructural observations were made on both an optical microscope and a scanning electron microscope. In addition, hardness measurements were made using the Vickers indenter and strength tests-a static compression test. Experiments have allowed us to determine the very important differences in both the nucleation and propagation of microcracks emerging after crossing the yield point between gravity-cast aluminum-silicon aluminum alloys.

Qualitative microstructure investigations of the AlSiMg alloy's microstructure in both its original state (with the characteristic primary structure) and after precipitation hardening revealed the significant heterogeneity of the eutectic phases concerning their shape, size, and distribution. An evaluation of the stereological parameters of the eutectic phases was carried out. The computer-image analysis was performed in order to define the fraction of the relative volume and shape of the eutectic phases and to establish their influence on the mechanical properties.