Eutectic Al-13 wt. % Si and hypereutectic Al-16 wt. % Si were prepared by using permanent mould casting technique. Effect of the cooling technique on the cast microstructure, mechanical properties, and electrical conductivity of Al-Si alloys was investigated by using the conventional water-cooled and air-cooled methods. The mechanical properties such as the yield stress, tensile strength, hardness, and impact energy were measured at various cooling methods. Microstructure with scanning electron microscope (SEM) and Energy dispersive spectrometer (EDS) analysis of Al-Si alloys have been studied. In addition, the hardness after solution treatment at 529 °C for 2 h and artificial ageing at various temperatures 180 °C and 210° C for aging time 2-10 h was measured. The results show enhancement in the mechanical and electrical properties for the eutectic Al-13 wt. % Si and hypereutectic Al-16 wt. % Si alloys for the water-cooled over the air-cooled technique. In addition, the largest value of the impact energy (4.91 J) was obtained for the eutectic Al-13 wt. % Si alloys compared to the hypereutectic Al-16 wt. % Si alloys at 3.09 J for watercooled-medium. The total solidification time (TST) of Al 13% wt. Si was longer than that time for the hypereutectic Al 16% wt. Si at various cooling mediums. Aging studies of Al-Si alloys with aging temperatures 180 ºC and 210 ºC show that the hardness values increased as the silicon content increases. For hypereutectic Al-16 wt. % Si at aging temperature 180 ºC and aging time 4 h by using water-cooled technique, it was observed that the maximum hardness value reached to 100 HRD compared that value was 87 HRD for the eutectic Al-13 wt. % Si alloy.
Several modifications have been made on friction stir welding process to overcome some certain limitations which have been reported. One of these modifications is to use ultrasonic energy as an assistance tool in FSW process. In the present paper, a mathematical model is developed to express the heat generation during ultrasonic vibration enhanced friction stir welding process (UVeFSW). A finite element model is built to perform a transient thermal heat transfer analysis using ANSYS mechanical APDL software package. The temperature contours, temperature distribution and the thermal cycles were predicted using the moving heat source technique. To validate the model, k-type thermocouples were used to measure the temperature and thermal cycles at five locations. The results showed a good agreement between the simulated and experimentally measured results.
A B S T R A C TT his paper investigated the moisture absorption, mechanical behavior and the dielectric performance of hybrid and non-hybrid polymeric composites. Hand lay-up technique was used for processing carbon; glass reinforced polyester resin composites (non-hybrid) and carbon-glass/polyester hybrid composites with various fiber configurations. The maximum resistance of water absorption was obtained for the hybrid composites with combinations [2C-2G], where the water absorption ratio reached to 1%. In addition, the maximum tensile, flexural strengths and ILSS of t his combination were 123 MPa, 1397 MPa, and 22.35 MPa, respectively. This is due to the higher tensile strength of polyester matrix and good adhesion between the glass and carbon fabrics with the polyester matrix. The dielectric constant of nonhybrid composite with codes [C] is higher than non-hybrid composite with codes [G] and dielectric constant for all hybrid composites lies between non -hybrid composites.
The effect of water absorption and swelling thickness on the tensile properties of flax/sisal/carbon/glass fabrics reinforced by unsaturated polyester-based hybrid composites was evaluated. Hybrid composites reinforced with different natural and synthetic fiber configurations have been processed using the Hand lay-up (HLU) technique. Water absorption test was carried out by immersing specimens in distilled water for different lengths of time, up to 1344 hours, and showed slight enhancement of water absorption for fibers configuration [
Unsaturated polyester-based composites and reinforced with three types of fabrics, E-glass, basalt, and carbon, were fabricated by Hand-Lay Up (HLU) technique at room temperature, with various fiber configuration. Monotonic mechanical properties of hybrid composites laminate such as the tensile, flexural, inter-laminer shear strength and impact strength were investigated. The dynamic response of hybrid laminates composite under pulse load was studied theoretically and experimentally. In the theoretical part, the validity of the theoretical model for evaluating natural frequencies, mode shapes and dynamic response of hybrid composite laminates at various staking sequence has been examined by utilizing of the finite element software (ANSYS). In the experimental part, the response of hybrid composite specimens with various types of fiber configuration and four types of boundary fixations was measured by hammer test technique "frequency response function" (FRF). The results show that the reinforcement by adding the basalt fabric and carbon fabric based unsaturated polyester composites as a fiber configuration [2C/B/2C] S enhanced the mechanical properties of the hybrid composite laminates among other various stacking sequences. For the stacking sequence [2C/B/2C] S , it was found that the largest values of tensile, flexural strength and interlaminar shear strength (ILSS) were 128.76 MPa, 405 MPa, 20.25 MPa, respectively. The results show the good bonding adhesion at the interface between the fibers and matrix of the hybrid composite laminates. The impact properties with stacking sequences [C-C-G-C-C]s have the largest value at 3.73 Joule as compared with the other composites and stacking sequences of all hybrid composite laminates. Also, the BFRP composites specimen gives the best vibration resistance compared to the other stacking sequences of hybrid composite laminates. The comparison between experimental and numerical model shows the efficiency of the proposed mathematical model of the composite structural specimen with bonded joints.
This study was carried out to examine the mechanical properties of hypereutectic Al-16% Si alloy with the introduction of zinc oxide (ZnO) nanoparticles (NPs) synthesized by simple sol-gel method. The microstructure of the synthesized ZnO NPs was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The microstructure of the synthesized ZnO NPs reflects the formation of the wurtzite-type ZnO and the average crystallite sizes around 35 nm. Hypereutectic Al-16% Si with varies concentration of ZnO NPs (0.5, 1, 1.5 and 3%) was synthesized utilizing permanent mold casting technique. Energy-dispersive spectrometer (EDS) and scanning electron microscopy (SEM) of hypereutectic Al-16 wt% Si alloys after the dispersion of these nanoparticles were analyzed. The results revealed that an addition of ZnO nanoparticle to hypereutectic Al-16wt % Si alloy enhanced the tensile strength, impact energy and the hardness. The maximum tensile strength, impact energy and hardness of this alloy was 200 MPa, 5.38 J, 60 BHN, respectively, which occurred at 3 wt% of ZnO NPs. This enhancement in mechanical properties can attributed to the decomposition and dissolution of the nano-oxide particles in aluminum alloy melt and grain growth restriction.
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