The semisolid processing technology is not widely used due to the high cost of raw material
and the equipment it requires. New low-cost raw materials and processes could be the key to expand
the use of this technology. This paper describes an initial effort to develop new Al-Si-Mg in terms of
raw material production and processing. The morphological evolution of all the alloys produced was
characterized during their reheating to the semisolid state at 45 and 60% solid fraction, as well as the
semisolid behaviour in terms of viscosity versus shear rate. The adaptation of the semisolid
technology to the thixoforming process via eccentric press was tested using an equipment up to 25
tons. This type of equipment is not commonly employed in this kind of processing. Results indicate
that alloys with low silicon content, e.g., 2 or 4wt%Si, behave similarly to alloys with 7wt%Si, which
are normally used in the thixoforming process, with a viscosity of about 2 * 105 Pa.s. The semisolid
behaviour of low silicon alloys indicates the potential expansion of the range of raw materials for this
application. Thixoforming of semisolid materials in an eccentric press appears to be a very promising
technology, yielding parts that, despite their simplicity and restricted shape, display a very good final
mechanical behaviour.
Thermally sprayed coatings are employed for many purposes, as corrosion protection, wear resistance improvement, resistance to high temperatures, and others. The coating performance depends on its morphology, which is composed by splats, pores, oxide inclusions, and entrapped unmelted or resolidified particles. In arc spray process (ASP), the heat source is the arc electric obtained from the contact of two consumable metallic wires with different electric potentials, and the carrier gas is the compressed air. The velocity, dimensions, and thermal characteristics of the droplets sprayed are related to the morphology and properties of the coating. The main goal of this research is to evaluate how the velocity, temperature, and particle size are modified by the chemical composition of different materials (carbon steel, stainless steels, and FeMnCrSiNi alloy). The intention is to predict how the modification of the process parameters will change the particles properties. The materials had similar behavior tendencies during the flight: the velocity increased to a peak value then decreased, but this maximum value was different for materials with different particle size. The particles’ size did not present significant differences during the flight; and the particles cooled down as they moved away from the gun, except the austenitic stainless steel and the FeMnCrSiNi alloy, which increased the droplets temperature during the travel. These alloys also presented more variation in chemical composition during flight.
Thixoforming technology has made considerable advances since its initial discovery in 1973. Although, after almost 40 years, few raw materials are still used as thixoforming materials. The Al-Si-Mg alloys often used for semi-solid state processing are notably casting alloys like A356 and A357. The development of new alloys specially tailored for thixoforming is a new challenge in this area of research. This paper will present some results related to the study of Al-2wt%Si-05wt%Mg and Al-4wt%Si-05wt%Mg alloy obtained via conventional foundry followed by ultra-refining. The results are compared with a commercial Al-7wt%Si-05wt%Mg alloy. Also presents its morphological evolution in the re-heating of the material to obtain the solid fraction of 45% and 60% in four different holding times 0, 30, 90 e 210 seconds. After re-heating, with the determination of grain size and globules, held the study Rheocast Quality Index (RQI) and Shape Factor (SF), parameter that helps to quantify the efficiency of the treatment globularization to obtain semi-solid structure with globular structure. The morphological evolution showed that the increase of holding time resulted in a minor increase in the globule size of the structure. The RQI values show that there is little morphological evolution in the treatment of globularization for alloys with percentage of Si, indicating alloys with percentage below of 4wt% Si is the most appropriate for thixoforming.
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