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This study aimed to determine effects of holding time on microstructure and shear strength of resistance spot-welded joints between mild steel and aluminum with zinc powder filler. The materials used are 0.9 mm thick mild steel, 1.2 mm thick 3000 series aluminum, and 200 mesh zinc powder. Welding parameters were selected as welding time of 0.5 seconds (s), electric currents of 8000 and 9000 A, with holding time variations of 1, 3, and 5 s. Macro and scanning electron microscope (SEM) images follow ASTM E3-01, while ASME IX was used as tensile test standards. The macro images showed that holding time affected quality of the welded joints. Applying a longer holding time was able to reduce defects on the welded joints. SEM energy-dispersive X-ray spectroscopy (SEM-EDX) analysis exhibited that the holding time of 1 s produced a lack of density in the spot-welded joint, resulting in the existence of porosity. In contrast, increasing the holding time to 5 s gives a denser spot-welded joint with no defects found. The tensile test results showed that applying electric current of 8000 A, welding time of 0.5 s, and holding time of 1 s produced the joint with the weakest shear strength of 130 N. The highest joint shear strength of 790 N is obtained with the condition: electric current of 9000 A, welding time of 0.5 s, and holding time of 5 s.

This paper aims to find the phase transformation of Ti-3Mo at% applying solid solution treatment. Methodology: the Ti-3Mo specimens were produced by using arc melting furnace followed by homogenization in vacuum capsule at 1200 o C for an hour. After that, the specimens were hot-rolled into 1.5 mm in thickness. Then, the specimens were solid solution treated at 1000 o C for 10 minutes followed by rapid cooling (quenching). Phase and microstructure observation were conducted using XRD and optical microscope. TEM was also used in this study. Vickers hardness test was applied to confirm the homogeneity of the specimens. Results: It was found that α''-martensite titanium with orthorhombic cell structure was the main phase of Ti-3Mo after solid solution treated followed by rapid cooling. Analysis of volume indicated that α''-martensite unit cell had similarity to β-phase titanium but 0.792% greater in volume. Further heat treatment needed to be applied in order to ensure the formation of β-phase in the specimen. Applications: This study shows that the presence of molybdenum element in titanium alloys can prevent the formation of α hexagonal close packed (hcp) phase at room temperature.

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