Variation of Microstructure and Mechanical Properties of ZW61 Magnesium Alloy Solidified under Different Pressures

There is little datum related to microstructure and properties of Mg alloys squeeze-casted with pressure over 200 MPa. In this study, the microstructure and properties of Mg-6Zn-1.4Y (ZW61) alloy solidified under 100MPa to 800MPa were investigated. The results show that a remarkable microstructure refinement and porosity reduction can be reached through solidification under high pressure. The average grain size and the volume fraction of second phase, i.e. quasicrystal I-phase, decrease continuously with the increase of applied pressure. The tensile properties, especially elongation, are obvious enhanced because of the microstructure refinement and castings densification under high pressure. The ultimate tensile strength and elongation of ZW61 alloy in as-cast state are 243 MPa and 18.7% when the applied pressure is 800 MPa, which are increased by 35% and 118% respectively, compared with that of the gravity castings.

Research on Mechanical and Electrical Properties of Cu-Ag Alloys Designed for the Construction of High Magnetic Field Generators

The individual sections, wiring and construction of electromagnet windings responsible for strong magnetic field impulses may be one application for hypoeutectic Cu-Ag alloys. High electrical properties and mechanical properties (tensile strength, yield strength, impact strength) as well as high heat, fatigue and rheological resistance are required for these kinds of applications due to the unique nature of such operations (strong vibrations of high frequency and amplitude resulting from Lorenz forces and the possibility of significant and rapid heating from Jule’s heat). The limited solubility of copper and silver in the solid state enables the effective modification of the alloys’ microstructure through heat treatment and further shaping of their high mechanical and electrical properties via cold plastic working. The article presents the manufacturing of Cu-Ag alloys with the weight percent of Ag between 3 and 7 using the continuous casting process along with research on the physicochemical, mechanical and electrical properties of the obtained casts. The research on the amount of plastic deformation and its influence on the wire drawing process and the mechanical and electrical properties of the wires is also discussed. The temperature coefficients of resistance were defined in order to determine the temperature influence on the electrical resistance changes dynamics. The microstructural analysis was carried out in the as-cast state. The preliminary research conducted indicates that the obtained Cu-Ag alloys in the as-cast state exhibit a set of high mechanical and electrical properties. The prospective next stage of research includes the selection of favourable heat treatment parameters which would provide optimally modified microstructure of the alloys, as well as determining the deformation coefficients allowing for further increases in the mechanical and electrical properties.

Kappa Carbide Precipitation in Duplex Fe-Al-Mn-Ni-C Low-Density Steel

The microstructural evolution of a Fe-Mn-Al-Ni-C low-density steel was studied. The lightweight low-density steels are a promising material for the transportation industry, due to their good mechanical properties and low density. The base microstructure of the investigated steel consists of ferrite and austenite. Thermo-Calc calculations showed the formation of an ordered BCC (body-centred cubic) B2 phase below 1181 °C and kappa carbides below 864 °C. The steel was produced in a vacuum induction furnace, cast into ingots and hot forged into bars. The forged bars were solution annealed and then isothermally annealed at 350, 450, 550, 650, 750, and 850 °C. The microstructure of the as-cast state, the hot forged state, solution annealed, and isothermally annealed were investigated by optical microscopy and scanning electron microscopy. The results showed the formation of kappa carbides and the ordered B2 phase. The kappa carbides appeared in the as-cast sample and at the grain boundaries of the isothermally annealed samples. At 550 °C, the kappa carbides began to form in the austenite phase and coarsened with increasing temperature.

THE INFLUENCE OF CHEMICAL COMPOSITION AND HEAT TREATMENT ON THE MECHANICAL PROPERTIES AND WORKABILITY OF THE ALUMINIUM ALLOY EN AW 5454

The influence of chemical composition and heat treatment on the mechanical properties and formability of the selected commercial aluminium alloy EN AW 5454 was investigated. The main properties of alloy 5454 from the AA 5xxx series are very good corrosion resistant and has good formability. From the cast slab a 50 mm thick slice was taken in the width cross section in the slab centre. One half of the slice was homogenised for 10 hours at a temperature of 530 °C. The cast and homogenised samples were investigated using light and scanning electron microscopy. For the study of the influence of the heat treatment, samples in the as-cast state were annealed in the laboratory furnace at a temperature of 530 °C for 4, 6, 8, 10 and 12 hours. To study the influence of chemical composition, four different samples were prepared: the first without additions, the second with an addition of 1 wt% Mn, the third with 3 wt% Mg and the fourth with an addition of both elements, Mn and Mg. The XRF analyses confirmed the desired chemical composition of all four produced alloys. Half of each alloy’s sample was homogenised at the same temperature and time as the base alloy in the as-cast state. The hot deformation behaviour of the different alloys was investigated using cylindrical hot compression tests performed on a Gleeble 1500D thermo-mechanical simulator. By comparing flow curves a high influence of the thermo-mechanical parameters on the alloy formability can be seen. The alloy has good workability and with the addition of Mn and Mg, the stress values are higher than those of the base alloy.

Effect of Short T6 Heat Treatment on the Thermal Conductivity and Mechanical Properties of Different Casting Processes Al-Si-Mg-Cu Alloys

The thermal conductivity of alloys is gradually becoming appreciated. It is often assumed that heat treatment can improve the thermal conductivity of Al-Si-Mg-Cu alloys, but there has been little relevant research. This paper studies the effects of different casting processes and short T6 heat treatment (ST6) on the thermal conductivity and mechanical properties of Al-Si-Mg-Cu alloys. The results show that a microstructure with fine α-Al crystal grains can be obtained by semi-solid die casting (SSDC), improving the mechanical properties of the Al-Si-Mg-Cu alloy in the as-cast state. After SSDC, the size and aspect ratio of eutectic silicon can be reduced by ST6 treatment, effectively improving the thermal conductivity and mechanical properties of the alloy. Finally, the influence of eutectic silicon on electron transport is analyzed in detail. With the SSDC + ST6 processing technology, Al-Si-Mg-Cu alloys with excellent thermal conductivity and mechanical properties can be obtained.

Increasing the Wear Resistance of Marine Diesel Engines Elements Made of Ductile Iron

This paper examines the influence of austempering and shot peening on the wear resistance of ductile iron. Samples for further testing were made from mechanically processed casts. The hardness and microstructure of ductile iron were examined on the prepared samples. Metallographic analysis of ductile cast iron samples in the cast state determined the pearlitic-ferritic structure of the matrix characteristic of this type of cast iron. Pearlite predominates in the structure, and the rest consists of ferrite and graphite nodules. The samples were then austempered. The isothermal conversion was 240 °C. After austempering, the hardness was measured and the microstructure was characterized, and the changes that occurred in relation to the heat-treated ductile iron were studied. Austempering created a new austempered structure, harder than that in the cast state, which led to improved mechanical properties. A needle-like structure of lower bainite (ADI) with high-carbon austenite, untransformed austenite, martensite and graphite nodules was achieved. The selected parameters of the shot peening process deformed the surface of the ADI and achieved a mostly martensitic structure without the presence of a soft phase, which increased resistance to abrasion. Additional hardening of the substrate by the shot peening process resulted in a composite material with the properties of comparative steel parts, which are lighter, cheaper and easier to manufacture, more resistant to wear and quieter in operation. Such material should have an even wider application in mechanical engineering, and thus in the construction of marine machinery and plants.

The effect of homogenization on microstructure and hardness of a large-scale high-aluminum Al4.4Co26Cr18Fe18Ni26Ti5.5 Compositionally Complex Alloy cast

As any largescale cast material, specific Compositionally Complex Alloys or High Entropy Superalloys contain segregations, leading to unideal, inhomogeneous properties. This work presents the effects of a homogenization heat treatment at 1 150°C for 6 h of a large-scale cast Al4.4Co26Cr18Fe18Ni26Ti5.5 alloy. In order to reveal these effects, homogenized specimens were analyzed and compared to the as-cast state with regard to chemical homogeneity as well as the homogeneity of elemental solution by means of scanning electron microscopy, energy dispersive X-ray spectroscopy as well as X-ray diffraction and hardness measurements. Despite the increased Al content, intermetallic phases and segregations, observable in the as-cast state, dissolve during homogenization. Improved, but not full homogeneity of elemental distribution after annealing can be determined. The improved state of solution and homogeneity agrees with the increasing lattice parameter from 3.572 Å to 3.594 Å and the decreasing hardness from 320.3 HV10 to 245.2 HV10 during homogenization.

Microstructural and Cavitation Erosion Behavior of the CuAlNi Shape Memory Alloy

Microstructural and cavitation erosion testing was carried out on Cu-12.8Al-4.1Ni (wt. %) shape memory alloy (SMA) samples produced by continuous casting followed by heat treatment consisting of solution annealing at 885 °C for 60 min and, later, water quenching. Cavitation resistance testing was applied using a standard ultrasonic vibratory cavitation set up with stationary specimen. Surface changes during the cavitation were monitored by metallographic analysis using an optical microscope (OM), atomic force microscope (AFM), and scanning electron microscope (SEM) as well as by weight measurements. The results revealed a martensite microstructure after both casting and quenching. Microhardness value was higher after water quenching than in the as-cast state. After 420 min of cavitation exposure, a negligible mass loss was noticed for both samples. Based on the obtained results, both samples showed excellent cavitation resistance. Mass loss and morphological analysis of the formed pits indicated better cavitation resistance for the as-cast state (L).

Preparation of Sub-Micron Bi Alloy Powers with the Ultrasonic Mixed Crushing

The powders of the BiInSn alloy were produced by the ultrasonic atomization and the ultrasonic mixed crushing using the different dispersants. In this study, the composition, microstructure, melting point, and size of these powders were observed. The viscosity of different solutions of the dispersants and the mechanical properties of the sintered bulk materials were also tested. From the data analysis and results, we found that the composition of the powders using the different methods was consistent with the as-cast state. In addition, the size of powder produced by ultrasonic mixed crushing was significantly smaller than that ultrasonic atomization. And during the ultrasonic crushing process, with the increase of the viscosity of the dispersant, the size of the final powder also decreased, and even submicron powder were produced. The product of submicron powder could effectively improve the density and mechanical properties of sintered materials. And the principles of ultrasonic atomization and ultrasonic mixed crushing were discussed. We found that the mechanism of ultrasonic mixed crushing to produce powder was the micro-shock-wave theory of ultrasonic cavitation. At the same time, these dispersants were effective in keeping the droplets separate from each other and preventing them from merging back into the larger droplets. The droplet was solidified into a powder by rapid cooling in the end.