In this study, modification of the AZ91 magnesium alloy surface layer with a CO2 continuous wave operation laser has been taken on. The
extent and character of structural changes generated in the surface layer of the material was being assessed on the basis of both macro- and
microscopy investigations, and the EDX analysis. Considerable changes in the structure of the AZ91 alloy surface layer and the
morphology of phases have been found. The remelting processing was accompanied by a strong refinement of the structure and a more
uniform distribution of individual phases. The conducted investigations showed that the remelting zone dimensions are a result of the
process parameters, and that they can be controlled by an appropriate combination of basic remelting parameters, i.e. the laser power, the
distance from the sample surface, and the scanning rate. The investigations and the obtained results revealed the possibility of an effective
modification of the AZ91 magnesium alloy surface layer in the process of remelting carried out with a CO2 laser beam.
Secondary or multiple remelted alloys are common materials used in foundries. For secondary (recycled) Al-Si-Cu alloys, the major problem is the increased iron presence. Iron is the most common impurity and with presence of other elements in alloy creates the intermetallic compounds, which may negatively affect the structure. The paper deals with effect of multiple remelting on the microstructure of the AlS9iCu3 alloy with increased iron content to about 1.4 wt. %. The evaluation of the microstructure is focused on the morphology of iron-base intermetallic phases in caste state, after the heat treatment (T5) and after natural aging. The occurrence of the sludge phases was also observed. From the obtained results can be concluded that the multiple remelting leads to change of chemical composition, changes in the final microstructure and also increases sludge phases formation. The use of heat treatment T5 led to a positive change of microstructure, while the effect of natural aging is beneficial only to the 3rd remelting.
Monitoring the solidification process is of great importance for understanding the quality of the melt, for controlling it, and for predicting the true properties of the alloy. Solidification is accompanied by the development of heat, the magnitude of which depends on the different phases occurring during solidification. Thermal analysis is now an important part of and tool for quality control, especially when using secondary aluminium alloys in the automotive industry. The effect of remelting on the change of crystallization of individual structural components of experimental AlSi9Cu3 alloy was determined by evaluation of cooling curves and their first derivatives. Structural analysis was evaluated using a scanning electron microscope. The effect of remelting was manifested especially in nucleation of phases rich in iron and copper. An increasing number of remelts had a negative effect after the fourth remelting, when harmful iron phases appeared in the structure in much larger dimensions.
The paper deals with the problem of multiple remelting influence on AlSi6Cu4 alloy modified by antimony on chosen mechanical characteristics, microstructure and gas content. This foundry alloy is used mostly in automotive industry. Foundry Aluminum-Silicon alloys are also used in number of industrial weight sensitive applications because of their low weight and very good castability and good mechanical properties. Modifiers are usually added to molten aluminum-silicon alloys to refine the eutectic phase particle shape and improve the mechanical properties of the final cast products and Al-Si alloys cast properties.
This article focuses on the study of the influence of remelting and subsequent natural and artificial ageing on the structure of recycled AlSi9Cu3 alloy with increased iron content. The assessed changes in eutectic silicon and iron-based intermetallic phases were carried out using optical and scanning electron microscopy. The degradation of the eutectic silicon morphology due to remelting occurred only at the highest numbers of remelting. The effect of remelting the investigated alloy, which is accompanied by a gradual increase in wt. % Fe, began to manifest significantly through a change in the length of the ferric phases after the fourth remelting. As expected, the artificial ageing process has proven to be more effective than natural ageing. It has led to a change in the eutectic silicon morphology and has been beneficial in reducing the lengths of adverse ferric phases. The use of alloys with higher numbers of remelting, or with greater “contamination”, for the manufacture of shape-challenging castings is possible when using a suitable method of eliminating the negative factors of the remelting process. The results of our investigation show a suitable method of the above elimination the application of heat treatment T5 – via artificial ageing.
Paper present a thermal analysis of laser heating and remelting of EN AC-48000 (EN AC-AlSi12CuNiMg) cast alloy used mainly for
casting pistons of internal combustion engines. Laser optics were arranged such that the impingement spot size on the material was a
circular with beam radius rb changes from 7 to 1500 m. The laser surface remelting was performed under argon flow. The resulting
temperature distribution, cooling rate distribution, temperature gradients and the depth of remelting are related to the laser power density
and scanning velocity. The formation of microstructure during solidification after laser surface remelting of tested alloy was explained.
Laser treatment of alloy tests were perform by changing the three parameters: the power of the laser beam, radius and crystallization rate.
The laser surface remelting needs the selection such selection of the parameters, which leads to a significant disintegration of the structure.
This method is able to increase surface hardness, for example in layered castings used for pistons in automotive engines.
What is the limit of improvement the structure obtained directly from the liquid state, with possible heat treatment (supersaturation and aging)? This question was posed by casting engineers who put arbitrary requirements on reducing the DAS (Dendrite Arm Spacing) length to less than a dozen microns. The results of tests related to modification of the surface microstructure of AlSi7Mg alloy casting treated by laser beam and the rapid remelting and solidification of the superficial casting zone, were presented in the paper. The local properties of the surface treated with a laser beam concerns only a thickness ranging from a fraction to a single mm. These local properties should be considered in the aspect of application on surfaces of non-machined castings. Then the excellent surface layer properties can be used. The tests were carried out on the surface of the casting, the surface layer obtained in contact with the metal mould, after the initial machining (several mm), was treated by the laser beam. It turned out that the refinement of the microstructure measured with the DAS value is not available in a different way, i.e. directly by casting. The experimental-simulation validation using the Calcosoft CAFE (Cellular Automaton Finite Element) code was applied.
The effect of laser processing on the structure, microstructure and hardness of high-speed steel produced by powder metallurgy was investigated. The samples were surfaces remelted with impulse CO2 laser radiation under different operation conditions. In the remelted layer, the presence of full remelting, partial remelting and heat affected zones was detected. As a result of concentrated laser beam treatment, microstructures characteristic of the rapid crystallization process were observed. The microstructure in the full remelting zone was characterized by a fine microdendritic structure with the average distance between the secondary axes of dendrites below 1 µm and the dissolution of primary carbides. Retained austenite was found in the remelted samples, the amounts of which depended on the treatment parameters and grew with an increase in the speed of the laser beam movement. There was no unequivocal effect of the distance of the irradiated surface from the focus of the beam focusing system on the content of retained austenite. Due to the presence of retained austenite in the remelted part, the hardness decreased by about 23% compared to the hardness of the material before the treatment. On the other hand, laser processing leads to strong refinement of the microstructure and eliminates the residual porosity of powder steels, which can increase the toughness and cutting performance of steel. The research also showed the possibility of shaping the geometry of the remelting zone by the appropriate selection of machining parameters
This study investigates the microstructures and the mechanical properties of equiatomic Ti20Mo20Ta20Nb20V20 and non-equiatomic Ti40Mo15Ta15Nb15V15 and Ti60Mo10Ta10Nb10V10 HEAs using X-ray diffraction (XRD) analysis, field emission scanning electron microscope (FE-SEM), and micro-Vickers hardness test. The specimens were fabricated using the vacuum arc remelting (VAR) process and homogenized at a temperature of 1300°C for 4 h in a vacuum atmosphere. The determined thermodynamic parameters, Ω ≥ 1.1, δ ≤ 6.6%, and VEC < 6.87, suggested that the HEAs consisted of BCC solid solutions. XRD patterns of all the HEAs displayed single BCC phases. The difference in the solidification rate led to the micro-segregation associated with the elements Ta and Mo enriched in the dendrite arms and the elements V and Ti in the inter-dendritic regions. The HEA specimens showed a decrease in hardness with higher concentration of Ti element because the intrinsic hardness of Ti is lower as compared to the intrinsic hardness of Nb and Mo.
In this study, low-carbon cast steel was reinforced with TiC by SHS-B method, also known as combustion synthesis during casting method. The composite zone was then subjected to surface remelting by Gas Tungsten Arc Welding (GTAW) method. The remelting operation was realized manually, at 150 A current magnitude. Microstructure, phase composition and hardness of remelted zone were investigated. XRD results reveal that the phases of the composite zone in initial state consist of TiC and Feα. Surface remelting resulted in formation of thick layers containing TiC carbides, Feα and Feγ. Microstructural examination has shown strong refinement of titanium carbides in remelted zone and complete dissolution of primary titanium carbides synthetized during casting. The average diameter of carbides was below 2 μm. The structural changes are induced by fast cooling which affects crystallization rate. The hardness (HV30) of the remelted layer was in the range between 250 HV and 425 HV, and was lower than hardness in initial state.
The paper presents the possibility of the usage of the concfocal microscope for define the type of tribological wear present during the technical dry friction on the testing machine of the pin-on-disc T-01M. The pin was a remelted high-speed steel and the disc was made from sintered carbides. The surface layer of the high-speed steel was remelted with the electric arc with different parameters. The intensity of the electric arc current was changed, the scanning speed and the single, overlapping remeltings were used. On the basis of the 3D, 2D view of the surface friction of the pin (made from the remelted high-speed steel), disc (made from the sintered carbides) and the surface roughness profile run along the marked line, the presence of the abrasive wear can be defined with the description of the elementary wear processes due to the abrasive and/or adhesive wear.
The work presents the results of the research and tests of the surface machining of the S355NL and X5CrNi18-10 steels with the concentraded stream of heat with the usage of the GTAW method. The surface layers of the tested steels were remelted with the electric arc using the current of the electric arc 50, 100, 150 and 200A.The machining was done in the atmosphere of argon with the constant speed of the welding head. A microscope examination was performed of the obtained structure and measurements of depth, width and hardness of the received surface layer were performed. Moreover the relation between the current of the electric arc and geometry of the remelted layers with their microhardness was examined.