Amir Bolouri

Effect of forming conditions on mechanical properties of rheoformed thin plates with microchannels using electromagnetic stirring

Rheoforming is a near net-shape manufacturing technology for fabricating components from light alloys in their semisolid states with improved mechanical properties. In this work, a feasibility study on the fabrication of Silafont 36 aluminum thin plates via rheoforming was conducted. The thin plates were fabricated under different experimental conditions, such as different solid fractions and punch pressures. Electromagnetic stirring was used to prepare a semisolid slurry of Silafont 36 aluminum alloy. Subsequently, the slurry was transferred to die sleeve and injected into the die cavity of the thin plate. The thin plates were successfully fabricated under the optimal conditions of 50% solid fraction and a rheoforming pressure of 130 MPa.

Processing of Low-Carbon Cast Steels for Offshore Structural Applications

Cast steels with carbon contents of approximately 0.05%, 0.1%, and 0.2% (low-carbon steels) were processed. The investigated steels were first cast. Fully lath martensite was obtained after austenitization and water quenching of the cast steels. The mechanical properties of ∼0.05% carbon steel did not significantly change after tempering at 500°C, 540°C, and 580°C. The strength of ∼0.1% carbon content steel decreased after tempering for 2 h to 3 h at 580°C, and then stabilized at longer tempering times of 6 h. The ductility remained almost constant through the processes. The Charpy impact energy increased when the tempering time was increased from 2 h to 4 h, but decreased remarkably after tempering for 6 h. By increasing the tempering temperature from 450°C to 550°C, the ductility of the ∼0.2% carbon content steel increased, followed by a drop at 600°C. The strength of this steel was the highest at 450°C, but decreased and stabilized at tempering temperatures of 500°C to 600°C. The Charpy impact energy increased monotonically and reached its highest value at 600°C. Finally, the applicability of the investigated cast steels for offshore structures was assessed in detail.

The effect of heat treatment on the mechanical properties of a low carbon steel (0.1%) for offshore structural application

In this study, a low carbon cast steel (0.1% C) alloy designed for offshore structures, and the mechanical properties of the alloy under different heat treatment cycles have been evaluated. The effect of austenitizing time on the austenite grain size was studied. Subsequently, the quenched samples with minimum austenite grain size subjected to tempering experiments at different tempering temperatures (450 °C, 550 °C, and 650 °C) and cooling rates (0.23, 36, and 50 °C/s) from the temperature. The results showed that by increasing the austenitizing time, the austenite grain size initially decreased and reached the minimum value with ASTM number of 6.35 and then followed by an increase. When the tempering temperature increased, yield and tensile strengths decreased, whereas the ductility properties improved. In addition, yield and tensile strengths were not affected by cooling rate from tempering temperature, whereas the ductility properties were slightly affected. The increase in tempering temperature significantly led to improvement in the toughness to fracture of the alloy. The effect of cooling rate on impact energy for the samples tempered at 450 °C and 550 °C was negligible. By the contrast, impact energy for the samples tempered at 650 °C was markedly affected by cooling rate, in which the highest value was achieved for a cooling rate of 50 °C/s.

Thin-Plate Forming by Thixo- and Rheoforging

Thin plates with a thickness of 1.2 mm are fabricated using two processes, thixoforging and rheoforging, which are semisolid forming techniques. The die design, formability, microstructure, and mechanical properties of the fabricated thin plates are analysed. A fan-shaped gate is designed by analysing the filling behaviour using semisolid material, and uniform filling behaviour of material is obtained by arranging nine overflows in product area. semisolid metal is prepared through a semisolid process in which reheating, a thixoprocess, and cooling with stirring, a rheoprocess, are applied. The semisolid material is injected into a forging die and is formed into thin plate at a punch speed of 300 mm/s and under a pressure of 100 MPa. Since semisolid material with a solid fraction below 45% has mainly small primary α-Al particles, the formability of the thin plate is improved. The formed thin plate also has good mechanical properties since the small and globular grains are evenly distributed. The thin plate formed from semisolid material with a solid fraction above 50% has poor mechanical properties owing to the large quantity of coarse primary α-Al particles. A rheoforged thin plate exhibits poorer mechanical properties than a thixoforged thin plate, but rheoforging produces a more precise thin plate.

Rheoforging of thin case for IT devices with optimal process parameters and new type die design

The latest trend in the cell phone component industry to use aluminium and magnesium alloys has resulted in the advanced processing technologies. Semi-solid forming process that is advantageous for the mass production of thin parts with complex shapes have been of interest as a promising tool for near net-shape manufacturing. This study describes a semi-solid forming process for the development of a 1 mm-thick cell phone case by using the rheological material prepared by electromagnetic stirring equipment. Thus, a new type of die design for indirect rheoforging was proposed to efficiently control the primary α-Al phase particles in the thin part under rheological conditions. Their microstructure and mechanical properties were investigated and compared to parts produced without electromagnetic stirring. Those products fabricated by electromagnetic stirring had better mechanical properties and globular microstructures than those fabricated without electromagnetic stirring. Several processing parameters such as punch velocity (30 mm/s), punch pressure (75–250 MPa), stirring time (10 s), and solid fraction (0–20%) were used. The optimal condition that resulted in a defect-free component with the improved mechanical properties was explained and discussed.