The samples of the as-cast AM60 magnesium alloy were subjected to Friction Stir Processing (FSP). The effect of FSP on the microstructure of AM60 magnesium alloy was analyzed using optical microscopy and X-ray analysis. Besides, the investigation of selected properties, i.e. hardness and resistance to abrasion wear, were carried out. The carried out investigations showed that FSP leads to more homogeneous microstructure and significant grain refinement. The average grain size in the stirred zone (SZ) was about 6-9 μm. in the thermomechanically affected zone (TMAZ), the elongated and deformed grains distributed along flow line were observed. The structural changes caused by FSP lead to an increase in microhardness and wear resistance of AM60 alloy in comparison to their non-treated equivalents. Preliminary results show that friction stir processing is a promising and an effective grain refinement technique.
Abstract. In this study, surface remelting treatment of the AZ91 magnesium alloy by means of welding using a non-consumable electrode in an inert gas shield was carried out. Three variants of surface treatment were used, i.e. the single torch variant with a single heat source without cooling down the samples, the single torch variant with a single heat source and a cooling system with liquid nitrogen, and the double welding torch variant with a double heat source in the torches operating in a tandem configuration. Experimental verification of the applied apparatus solutions was based on both macro-and microstructural assessment of the obtained effects. Comparative analysis of the variants used and the obtained microstructural results allowed the authors to indicate the deficiencies and limitations of particular solutions and to single out the best solution that would be useful for modifying the surface layers of magnesium alloys, as well as other materials having a strong oxygen affinity.Key words: remelting treatment, GTAW technology, AZ91 magnesium alloy.Surface modification of AZ91 magnesium alloy using GTAW technology [14][15][16][17][18][19]. To this end, both lasers with continuous operation characteristics and pulse lasers are used. Among the advantages of using the laser beam one can mention is the short time of process execution, the possibility of precise concentration of the beam on a particular surface, as well as obtaining high temperature gradients in the material. The use of methods that are alternative to laser technologies, e.g. conventional welding arc heat sources, is sporadic. Difficulties may occur during the remelting treatment carried out by means of welding methods. Those difficulties are often the effect of the physical and chemical properties of magnesium and magnesium alloys, and particularly their strong oxygen affinity, whose consequence is the presence of a compacted, non-conductive MgO oxide layer on the material surface. Until recently, welding heat sources were used almost only for joining materials and their regeneration. This situation has been systematically changing in recent years. The GTAW method has been used, among others, by the authors of study [20], who subjected the AK7 aluminium alloy to surface treatment. The favourable microstructural changes triggered by remelting of the alloy resulted in an increase in hardness and resistance to abrasion. In turn, in study [21] iron castings were subjected to GTAW method treatment, and equally satisfactory treatment results were obtained. The GTAW method was used also by D. Wenbin et al. in study [22] to form a composite structure in the surface layer of the AZ31 magnesium alloy. Within this study assessment of the GTAW method effectiveness in the remelting treatment of the AZ91 magnesium alloy surface layer was conducted, as well as the comparative analysis of various apparatus and parameter variants.
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