Micro hardness

Friction stir welding (FSW) process is a promising solid-state joining process with the potential to join low-melting point material, particularly, aluminium alloy. The most attractive reason for joining aluminium alloy with this process is the avoidance of the solidification defects formed by conventional fusion welding processes. In this research article, an attempt has been made to develop an empirical relationship between FSW variables and Micro Hardness. A factorial design was used by considering three factor and eight trials, which enables to quantify the direct and interactive effect of three numeric factors, that is, tool rotational speed, welding speed, and shoulder diameter on the Micro Hardness. The developed relationship is useful for prediction of Micro Hardness in friction stir welded AA6061 aluminium alloy joints at 95% confidence level. It will also be helpful for selection of process variable to obtain the desired strength of the joint. Furthermore, the optimized capabilities in design-expert software were used to numerically optimize the input parameters. I. INTRODUCTION In many industrial applications steel is readily replaced by non-ferrous alloy, in most cases aluminium alloys. Some of these materials combine mechanical strength comparable with structural steel and low weight, allowing for a significant reduction of weight. But the joining of aluminium alloys can sometimes cause a serious problem by the conventional welding process. The difficulty is often attributed to the solidification process and structure including loss of alloying elements and presence of segregation and porosities. Friction stir welding (FSW) offers an alternative through solid-state bonding, which eliminates all these problems of solidification associated with the conventional fusion welding processes. The dependence on friction and plastic work for the heat source precludes significant melting in the work piece, avoiding many of the difficulties arising from a change in states, such as changes in gas solubility and volumetric changes, which often plague fusion welding processes. Further, the reduced welding temperature makes possible dramatically lower distortion and residual stresses, enabling improved fatigue performance and new construction techniques and making possible the welding of very thin and thick materials. FSW has also been shown to eliminate or dramatically reduce the formation of hazardous fumes and reduces energy consumption during welding, reducing the environmental impact of the joining process. Further, FSW can be used in any orientation without regard to the influence of gravitational effects on the process. These distinctions from conventional arc welding processes make FSW a valuable manufacturing process with undeniable technical, economic, and environmental benefits. The process and the terminology are schematically explained in Fig: 1.1. The welding process parameters such as tool rotational speed, welding speed, and pin diameter play a major role in deciding the weld quality. In general, the solid-state nature of the FSW process, combined with its unusual tool and asymmetric nature, results in a highly characteristic microstructure. The microstructure can be broken up into the following zones as explained in Fig: 1.2.

The chilled casting method is widely used in the metal casting industry to accelerate the mold's cooling rate. This method is very suitable for surface hardening by depositing the elements contained in the chill material onto the surface of the object being cast. One of the factors that influence surface hardness characteristics is the diffusion temperature. This study aims to determine the microhardness, surface layer thickness, and the element contained on the surface. The main material produced into Y-Block is ductile cast iron, the chill material is SS 304 plate with a thickness of 0.2mm. However, before the liquid material is poured into a mold, the chill plate is inserted into the surface of the pattern in the mold, then the plate was preheated. The result showed that the highest preheating temperature has produced microstructure around the surface area namely eutectic carbide of (FeCr)7C3, and (FeCr)3C. SEM-EDX analysis shows that 7.13%Cr is contained on the coating layer...

The influence of nature and pressure of ambient environment on the surface modification, plasma parameters, hardness, and corrosion resistance of Mg-alloy has been investigated. Nd: YAG laser (1064 nm, 10 ns, 25 mJ) at a fluence of 1.3 J cm −2 has been employed as an irradiation source. Targets of Mg-alloy were exposed in the ambient environments of argon (Ar), neon (Ne), and helium (He) at pressures ranging from 5 to 760 Torr. Scanning electron microscope has been employed to investigate the surface morphology of the irradiated targets. It reveals the formation of cavities, cones, droplets, ripples, and islands on the surface of the irradiated sample. Laser-induced breakdown spectroscopy technique was employed to measure electron temperature (T e) and electron number density (N e) of Mg-alloy. The value of electron temperature ranges from 6628 to 12,855 K, whereas the value of electron number density varies from 5.4 × 10 17 to 19.2 × 10 17 cm −3. The maximum T e and N e are observed in Ar and minimum in case of He. It was also revealed that both the surface morphology and plasma parameters are strongly dependent upon nature and pressure of environmental gases. The maxima of T e is achieved at a pressure of 10 Torr for all the three ambient environments that is, Ar, Ne, and He; whereas maxima of N e is achieved at different pressures, that is, at 760 Torr for Ar, at 200 Torr for Ne, and at 50 Torr for He. The hardness and corrosion resistance of irradiated Mg-alloy have been explored using Vickers Micro-hardness tester and Potentio-dynamic polarization technique, respectively. It was investigated that as compared with un-irradiated target, the hardness as well as corrosion resistance of the laser-irradiated target has been increased significantly in all environments. Plasma parameters, mechanical, and electrical properties of laser-irradiated Mg-alloy have been correlated with induced surface modifications and are strongly influenced by environmental conditions.

In this study the changes in HU values in dependence with process parameters and the layers’ sequence deposition – carbide and nitride, are studied. The multilayered coatings are condensates on 9XC and X12M alloyed tool steels’ substrates. The coating kinds are TiN/TiC/…and TiC/TiN/…. The latter are prepared in vacuum chamber by magnetron sputtering using VT3-1 target and consecutive introducing CH4 и N2 reactive gases. A computerized Nanoindentor is used for the hardness measurements.