International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Defects in die castings can include underfilling, blistering, sticking to the mold, and cracking. However, the factor that most affects the quality of castings is porosity. The primary causes of porosity are gaseous impurities and improper mold venting, which lead to gaseous porosity. Additionally, a poorly selected gating system, low casting speed, excessively short piston paths, low post-pressure, and low casting temperatures all contribute to shrinkage porosity. An additional factor contributing to the occurrence of pores is the increasing proportion of scrap (from production and post-production), which contains a wide variety of impurities. Gaseous inclusions (e.g., hydrides) can be removed from the liquid alloy by refining it, but metallic impurities are worse. In Al-Si alloys, one of the most detrimental elements is iron, which enters solution due to its low solubility in the solid state, at levels exceeding 0.6 wt%. At high percentages, it crystallizes in morphologically unfavorable phases, which deteriorate service properties, increase brittleness and porosity of castings, and limit their use.
This paper presents the results of a study of the effect of increased iron content (from 0.8wt.% to 1.5wt.%, in 0.2wt.% increments) on the porosity of AlSi7Mg alloy die castings. Porosity evaluation, conducted using microscopic metallography methods, was performed both qualitatively and quantitatively. It was found that the unfavorable morphology and dimensions of the Al5FeSi phase hinder the free flow of liquid alloy at the crystallization front. The lamellar-ligneous separations “close” the space between the dendrites of the α(Al) solid solution, causing the formation of shrinkage porosity. Increasing the iron content of die-cast Al-Si alloys forces the use of higher doping pressures, but not enough to cause “ejaculations” of the alloy in the dividing plane of the casting mold.

The paper presents the results of an investigation focused on the analysis of the wear of moulds for high-pressure casting with Al alloy. In order to repair and refurbish the mould parts of moulds for high-pressure casting of aluminium alloys, samples of experimental welds were prepared on the base material of grade 1.2343 (Dievar) of dimensions 150x130x30 mm refined to the hardness value of 44-48 HRC. A TruDisk 4002 solid-state disk laser with BEO D70 focusing optics was used for surfacing. Mat.No.1.2343 (Dievar), Mat.No.1.6356 (Dratec) and Mat.No.1.6356 (UTPA 702 and NIFIL NiCu7/Dievar) wires were used as additional material. Light microscopy technique was used to inspect the microstructures on the cross-sections of the welds. Microhardness measurements were performed with a Vickers indenter at a load of 500 g and a mutual indentation distance of 0.4 mm between the indenter impressions.

CMT technology provides significant advantages, such as reduced deformation due to high temperatures, high welding speed and a significant reduction in spatter compared to the MIG/MAG method. The experimental work was focused on verifying the possibility of renovating the surfaces of molds for high-pressure aluminum casting using CMT technology. A mold wear analysis was performed and a method of restoring functional surfaces was proposed. Two types of additive materials were used – Thermanit 625 and Thermanit X. The quality of the layers was evaluated by SEM, EDX microanalysis and the coefficients of friction of the layers were determined by the Ball-ondisc method. The renovation layers were also subjected to an immersion test in Al alloy at 680 °C.

The paper presents the results of research focused on the renovation of worn surfaces. Four progressive welding technologies were used – Cold Metal Transfer, MIG Pulse, TOP-TIG and laser technology. The layers were evaluated by non-destructive tests – visual, capillary and ultrasonic methods. The layers were evaluated under dry-friction adhesive wear conditions by the Ball-On-Disc method. A Si3N4 bead was used. Analyzes confirmed the impact of the renovation method on the quality of the resulting surface.

Molds designed for high-pressure casting of aluminum are exposed to very intense thermal, mechanical but also chemical stress during their operation. This stress leads to a synergistic effect of a combination of high-temperature corrosion processes in molten metals, under real conditions associated with mechanical wear. High-temperature corrosion in the environment of liquid metals occurs in the foundry industry, when casting molten metal most often into steel molds. Repair of worn parts of molds by welding, which can be performed even after their irreversible surface degradation, is a very efficient, cost-effective and envi-ronmentally acceptable form of their maintenance, while the chemical and physical properties are welded layers if they exceed the properties of the original material.

The paper focuses on the degradation of molds that are used for the technology of high-pressure casting of Al and its alloys. The method of high-pressure casting of aluminum products is one of the widely used production methods, which at the same time meets the requirements for precision and productivity in the production of cars and various mechanical parts. In the high-pressure casting process, the molds are exposed to various thermal and mechanical loads, where the molds and their shaped parts are degraded. The paper presents the results of research focused on the use of duplex PVD coatings to increase the life of shaped parts of molds for high-pressure casting of Al and its alloys.