No abstract

TiC and TiB2compounds in the form of interpenetrating network reinforced AZ91D magnesium matrix composites have been successfully synthesized by anin-situreactive infiltration technique. In this process, the ceramic reinforcement phases, TiC and TiB2, were synthesizedin-situfrom elemental powders of Ti and B4C without any addition of a third metal powder such as Al. The molten Mg alloy infiltrates the preform of Tipand B4Cpby the capillary force. The microstructure and reaction mechanism are investigated using SEM/EDS and XRD analysis. The results show that the processing parameters such as temperature, holding time and the green compact relative density have a significant influence on the reaction mechanism and the fabrication of the composite. In addition, the infiltrated Mg acts as an intermediary that makes the reaction possible at a lower temperature than that required for solid-state reaction between Ti and B4C. Microstructural characterization reveals a relatively uniform distribution of the reinforcing phases, TiC and TiB2in the Mg matrix.

In this paper, a practical and cost‐effective processing route, in situ reactive infiltration technique, was utilized to fabricate magnesium matrix composites reinforced with a network of TiC–TiB2 particulates. These ceramic reinforcement phases were synthesized in situ from Ti and B4C powders without any addition of a third metal powder such as Al. The molten Mg alloy infiltrates the preform of (Tip + B4Cp) by capillary forces. The microstructure of the composites was investigated using scanning electron microscope (SEM)/energy dispersive X‐ray spectroscopy (EDS). The compression behavior of the composites processed at different conditions was investigated. Also, the flexural strength behavior was assessed through the four‐point‐bending test at room temperature. Microstructural characterization of the (TiB2–TiC)/AZ91D composite processed at 900 °C for 1.5 h shows a relatively uniform distribution of TiB2 and TiC particulates in the matrix material resulting in the highest compressive strength and Young's modulus. Compared with those of the unreinforced AZ91D Mg alloy, the elastic modulus, flexural and compressive strengths of the composite are greatly improved. In contrast, the ductility is lower than that of the unreinforced AZ91D Mg alloy. However, this lower ductility was improved by the addition of MgH2 powder in the preform. Secondary scanning electron microscopy was used to investigate the fracture surfaces after the flexural strength test. The composites show signs of mixed fracture; cleavage regions and some dimpling. In addition, microcracks observed in the matrix show that the failure might have initiated in the matrix rather than from the reinforcing particulates.

This paper presents the optimization of welding parameters of electron beam welded joint of dissimilar materials namely AISI 304 stainless steel and AISI 1020 low carbon steel (0.21% C.). Three main welding parameters were investigated. These parameters are welding current, focusing current, and welding speed. The optimization was based, from one hand, on microstructure analysis of both bead and heat affected zones, using optical and scanning electron microscopes, and, from the other hand, the evaluation of tensile, impact, and micro-hardness mechanical properties. The results of the investigation showed that, an optimum welding current of 19 mA, a focusing current of 875 mA, and a welding speed of 8mm/s at a working distance 100 mm can provide uniform welding bead with full penetration, without undercuts and a narrow width of HAZ in the order of 2.3 mm. Moreover, they can secure a tensile failure outside the joint, in the base metal (low carbon steel) satisfying a tensile strength of about 430 MPa. Furthermore, the impact resistance of the joint was found to provide about 160 J/cm 2 (hummer against the root of bead) and about 70 J/cm 2 (hummer against the face of bead). The hardness distribution along the joint from the stainless steel side to the low carbon steel side through the bead and HAZ was determined, and indicates that, a maximum hardness of about 380 HV was obtained in the center of the bead. This value is higher than the obtained hardness values of both the austenitic stainless steel and low carbon steel.

A novel magnesium magnesium alloy was prepared by adding titanium and barium carbide under argon environment. The mechanical properties of the prepared alloy were investigated with respect to the AZ91D alloy. The microstructure of the composites was investigated using Scanning Electron Microscope SEM/EDS and X-ray diffraction (XRD). The corrosion behaviour of magnesium matrix composites reinforced with a Titanium and boron network of particulates fabricated using a low cost in-situ reactive infiltration technique. The corrosion behaviour was examined using both AC and DC techniques; electrochemical impedance spectroscope (EIS) and potentiodynamic polarization in dilute Harrison solutions. The tafel extrapolation results showed that the corrosion rate reduce by an order of magnitude. Moreover; EIS results shows that addition of Ti and Barium carbide improve the corrosion behaviour of AZ91 alloy and no sign of corrosion was appeared during 10 days of immersion in corrosive environments.