The paper concerns the problem of discontinuity in high pressure die castings (HPDC). The compactness of their structure is not perfect, as it is sometimes believed. The discontinuities present in these castings are the porosity as follow: shrinkage and gas (hydrogen and gas-air occlusions) origin. The mixed gas and shrinkage nature of porosity makes it difficult to identify and indicate the dominant source. The selected parameters of metallurgical quality of AlSi9Cu3 alloy before and after refining and the gravity castings samples (as DI - density index method), were tested and evaluated. This alloy was served to cast the test casting by HPDC method. The penetrating testing (PT) and metallographic study of both kinds of castings were realized. The application of the NF&S simulation system allowed virtually to indicate the porosity zones at risk of a particular type in gravity and high-pressure-die-castings. The comparing of these results with the experiment allowed to conclude about NF&S models validation. The validity of hypotheses concerning the mechanisms of formation and development of porosity in HPDC casting were also analyzed

MATEC Web of Conferences, open access proceedings in Materials science, Engineering and Chemistry

Discontinuities in cast products, obtained from a liquid state of an alloy, are the result of phenomena occurring during multiphase system crystallization. On the one hand, compacted defects as a shrinkage pipe are relatively easy to eliminate. On the other hand, it is known that presence of fine shrinkage and gas porosity is unavoidable. Detectability of these dispersed discontinuities depends on type of inspection method applied. Structure, including intensity and location of porosity zones, is dependent on the type of the alloy, casting configuration and conception of technological solution, related with control of velocity of the heat extraction to the mould. Thus, mechanical properties in the volume of a casting are not homogenous and are strongly reduced only in the zones of porosity. However, in strength calculations of cast products, this obvious fact is not taken into consideration. The rule of material homogeneity is applied instead, along with drastic increase of factor of safety. The paper indicates benefits of precise determination of limits of porosity zones located in the casting, using the NTD methods (for example, Phased Array ultrasonic tomography). Coordinates of porosity zones in 3D, introduced into CAD geometry and assigned with different properties allow to estimate the actual state of stress and strain of real object using FEM methods (systems like Ansys, Comsol). Load justified by operating conditions and application of tolerance of damage rule, with simultaneous reference to the limited state of stress according to LOV (Loss of Volume) and LEFM (Linear Elastic Fracture Mechanics) methods should find their place in design procedures of cast products, which will allow for better use of material and reduction of weight of the casting. This approach, named Tolerance of damage concerning the castings is the motto of this paper.

The paper presents study results focused on the microstructural, mechanical, and physicochemical properties of B-Cr coatings obtained by means of modification of diffusion borochromized layers by diode laser beam. The studies were conducted on 145Cr6 tool steel. Diffusion borochromized layers were produced at 950 °C in powder mixture containing boron carbides as a source of boron and ferrochrome as a source of chromium. In the next step these layers were remelted using laser beam. Powers: 600, 900, and 1200 W were used during these processes. The microstructure, microhardness, chemical composition, as well as wear and corrosion resistance of newly-formed B-Cr coatings were determined. As a result of laser beam interaction, the diffusion borochromized layer was mixed with the steel substrate. The study showed that too low laser beam power causes cracks in the newly formed B-Cr coating, and on the other hand, too higher laser beam power causes deep remelting resulting in the loss of microhardness. The reduced corrosion resistance in comparison with diffusion borochromized layers was caused by occurrence cracks or deep remelting. For B-Cr coatings produced using laser beam power 600 W, a small decrease in wear resistance was observed, but note that this coating was much thicker than diffusion borochromized layers. On the other hand, laser beam power of 1200 W caused a significant decrease in wear resistance. Newly formed B-Cr coatings had an advantageous microhardness gradient between the layer and the substrate.