This paper is devoted to the possibility of increasing the mechanical properties (tensile strength, yield strength, elongation and hardness) of high pressure die casting (HPDC) hypoeutectic Al-Si alloys by high melting point elements: chromium, molybdenum, vanadium and tungsten. EN AC-46000 alloy was used as a base alloy. The paper presents the effect of Cr, Mo, V and W on the crystallization process and the microstructure of HPDC aluminum alloy as well as an alloy from the shell mold. Thermal and derivative analysis was used to study the crystallization process. The possibility of increasing the mechanical properties of HPDC hypoeutectic alloy by addition of high-melting point elements has been demonstrated.
The paper presents the results of microstructure tests of EN AC-46000 hypoeutectic Al–Si alloy with and without high-melting-point elements: chromium, molybdenum, vanadium, and tungsten. The above-mentioned elements were used individually or simultaneously in various combinations. The tested castings were made using two technologies: shell molding and high pressure die casting (HPDC). Using X-ray diffraction and microanalysis of the chemical composition an attempt to determine the phase structure of the tested alloy was made. It has been shown that the microstructure of the base alloy consists of dendrites of α(Al) solid solution and complex eutectic mixtures: ternary α(Al) + Al15(Fe,Mn)3Si2 + β(Si) and quaternary α(Al) + Al2Cu + AlSiCuFeMgMnNi + β(Si). High-melting point elements, regardless of the combination used, attach mainly to intermetallic phases rich in Fe and form the Al15(Fe,Mn,M)3Si2 phase, where M is any high melting point element or a combination of such elements. It has been shown that the area fraction of the above-mentioned phase increases with increasing content of high melting point elements. A greater area fraction of the Al15(Fe,Mn,M)3Si2 phase in the casting from the shell mold in relation to the high pressure die casting has been also found.
Quaternary powder mixtures yNi–20Cr–1.5Al–xTiCp (y = 78.5, 73.5, 68.5; x = 0, 5, 10) were deposited on ferritic 10CrMo9–10 steel to form on plates ex-situ composite coatings with austenitic-based matrix. Plasma deposition was carried out with various parameters to obtain eight variants. The microstructure, chemical composition, phase constitution, phase transformation temperatures, and microhardness of the two reference TiCp-free coatings and six ex-situ composites were investigated by X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, thermodynamic simulation, and Vickers microhardness measurements. All composites had an austenite matrix with lattice parameter a = 3.5891–3.6062 Å, calculated according to the Nelson–Riley extrapolation. Microstructural observations revealed irregular distribution of TiCp in the composites. Large particles generally occurred near the external surface due to the acting buoyancy effect, whereas in the interior smaller particles, with an equivalent radius around 0.2–0.6 μm, were present. Due to initial differences in the chemical composition of powder mixtures and also subsequent intensive mixing with the low-alloy steel in the liquid pool, the matrix of the composites was characterized by various chemical compositions with a dominating iron concentration. Interaction of TiCp with matrix during deposition led to the formation of nano-precipitates of M23C6 carbides at the interfaces. Based on the ThermoCalc simulation, the highest solidus and liquidus temperatures of the matrix were calculated to be for the composite fabricated by deposition of 73.5Ni–20Cr–1.5Al–5TiCp powder mixture at I = 130 A. The mean microhardness of the TiCp-free coatings was in the range 138–146 μHV0.1, whereas composites had hardnesses at least 50% higher, depending on the initial content of TiCp.
Silicon carbide particles-reinforced Al4Cu composites containing 2.5, 5 and 7.5 wt.% of reinforcement were fabricated using powder metallurgy (PM) technique. The sintered Al4Cu-SiC composites were solution treated for 6 h at two different temperatures (495 and 530°C) and then aged at 180°C for various aging periods (4, 12 and 24 h). Effects of heat treatment on the microstructural changes and microhardness were investigated by scanning electron microscope, transmission electron microscope, x-ray diffraction and microhardness tests. The results indicate the ceramic particles-reinforced Al4Cu matrix requires different heat treatment parameters compared to the unreinforced alloy. The applied solution temperature did not allow for thorough dissolution of alloy phases in the matrix material produced by PM route. However, in Al4Cu-SiC composites the main strengthening phase (Al 2 Cu) was uniformly distributed in the matrix. The solid-solution temperature increase affects the reduction in time to reach peak hardness. The highest increment in microhardness by aging treatment was observed for composite with the addition of 5 wt.% of SiC solution treated at 530°C for 12 h (110 HV0.05).
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