Volume 54, Issue 4

The effect of welding speed on the weld seam profile in MAG and TIG/MAG hybrid arc welding was investigated in a low carbon steel. AISI 1020 steel materials having 5 mm thickness were used in the experiments. A fixed MAG and TIG welding currents (90 A and 100 A, respectively) and three different welding speeds (0.14, 0.21 and 0.30 m/min) were selected for welding process for a 100 mm long weld. The welded specimens were cut into several cross-sections; then metallographic tests were performed. The effect of TIG/MAG hybrid arc welding process was compared with the conventional MAG welding. The study showed that welding speed and the selected method have influence on the penetration and that the ratio of penetration depth / weld seam width is increased with increasing welding speed. This increase is more pronounced in TIG/MAG hybrid arc welding compared to conventional MAG welding. The microstructure of the weld metal was also changed relatively by variation of welding speed. With all welding parameters, the weld metal hardness is higher than hardness of the HAZ and the base metal.

Primary particles with faceted cubic morphology were produced in as-cast Al-Mg alloy due to the addition of Sc. The cross-section of the particles revealed some eutectic structure composed of multilayer of ‘Al 3 Sc + α-Al + Al 3 Sc····’. At the cooling rate of 200 – 300 K/s, Al 3 Sc primary phase nucleated initially on oxides within the melt and developed to a cubic structure with a ‘cellular-dendritic’ mode of growth. The formation of α-Al structural shells was attributed as a reason for the segregation of Mg-rich lamellar dendrites at later stages. A growth mechanism for multilayer structure was proposed using the results presented.

In this study, the effects of retrogression and re-aging (RRA) heat treatment applied on AA7075 aluminum alloy at various times and temperatures on the intergranular corrosion (IGC) behavior were investigated. The IGC solution was prepared according to ASTM G110 – 92 standard and the samples were kept in the solution for 24 hours. Susceptibility of the alloy to IGC was determined by weight loss detection, macro and microstructure studies. Scanning electron microscope (SEM) analysis was also performed. According to the results obtained, it was determined that the RRA processes in the AA7075 alloy change the grain boundary morphology and decrease the IGC corrosion susceptibility.

In the last fifteen years computer-tomography has proven to be a valuable aid in the fields of medicine, materials technology and forensics. Nowadays it is hard to image non-destructive testing being carried out without its use. This article serves to demonstrate the power of the technique within the field of failure analysis with reference to two chosen case studies. The first case concerns the failure of magnetic valves, the second case focusses on the failure of corrosion resistant screws.