The effect of the rheocast process on the microstructure and mechanical properties of Al-5.7Si-2Cu-0.3Mg alloy

This study shows the results of an experimental investigation of semisolid rheocasting of Al-5.7Si-2Cu-0.3Mg alloy using a cooling slope (CS) casting technique. However, the challenge is to determine process parameters of the CS process to get a desirable microstructure in the semisolid feedstock material. cooling slope technique was employed to create feedstock material for thixoforming under an argon gas atmosphere, where on an inclined plate that was fixed at a 60° slope angle, molten alloy is poured at different temperatures of 640°C, 650°C and 660°C at lengths 300, 400 and 500 mm. Examination the microstructure with optical microscope observed that the microstructure of conventionally cast alloy presented coarse and dendritic primary α-Al phase, whereas rheocast alloy included fine and nondendritic primary α-Al phase with homogeneous distribution of eutectic phase. The best CS processing condition has been identified for optimum pouring temperature of 650°C and the slope length of 400 mm as average globular grain size of around 31.67 ± 3 μm and a shape factor of about 0.66 ± 0.09 were obtained. The mechanical properties of conventional cast alloy were enhanced by the CS casting process. The ultimate tensile strength, the yield strength and elongation of the rheocast alloy were increased by 10%, 12% and 22% respectively compared to the conventional cast alloy. due to a reduction in shrinkage and porosity of the microstructure of the CS alloy

Dry sliding wear behavior of untreated and treated sugar palm fiber filled phenolic composites using factorial technique

The purpose of the current work was to investigate, for the first time, the potential improvements in the wear resistance of phenolic matrix composites from using sugar palm fiber (SPF) as a reinforcement. Con- sequently, open a new approach for utilizing the available locally cheap and non-toxic fibres to produce a prospective candidate tribo-materials for friction application, such as brake pad composites. The fibers were treated with seawater for 30 days and with a 0.5% alkaline solution to improve the fiber-matrix adhesion. Thereafter, the fibers were used in particle form with a volume loading of 30% to fabricate the samples using a hot press machine. The tribology-properties of the developed composites were tested using a computerized pin on disc machine. The test set-up was conducted for various combinations of different parameters, such as the type of treatment, applied normal load (30, 50, and 70 N), and sliding speed (2.6, 3.9, and 5.2 m/s) at a constant sliding distance of 5000 m under dry sliding conditions. Factorial technique, along with ANOVA analysis, were used to identify the significant and important design factors. The results depict that the volume loss of the seawater and alkali treated composites decreased by about 20.2% and 37.9%, respectively, whereas the coefficient of friction reduced by 10% and 13%, respectively, compared to the untreated composite. Moreover, ANOVA analysis revealed that the applied normal load and treatment made the most significant contribution to the volume, while the sliding speed had no significant effect on the wear results. Worn surface morphology investigation was carried out to support the results

Microstructure and Mechanical Properties of Thixowelded AISI D2 Tool Steel

Rigid perpetual joining of materials is one of the main demands in most of the manufacturing and assembling industries. AISI D2 cold work tool steels is commonly known as non-weldable metal that a high quality joint of this kind of material can be hardly achieved and almost impossible by conventional welding. In this study, a novel thixowelding technology was proposed for joining of AISI D2 tool steel. The effect of joining temperature, holding time and post-weld heat treatment on microstructural features and mechanical properties were also investigated. Acceptable joints without defect were achieved through the welding temperature of 1300 °C, while the welding at lower temperature resulted in a series of cracks across the entire joint that led to spontaneous fracture after joining. Tensile test results showed that maximum joint tensile strength of 271 MPa was achieved at 1300 °C and 10 min holding time, which was 35% of that of D2 base metal. Meanwhile, tensile strength of the joined parts after heat treatment showed a significant improvement over the non-heat treated condition with 560 MPa, i.e., about 70% of that of the strength value of the D2 base metal. This improvement in the tensile strength attributed to the dissolution of some amounts of eutectic chromium carbides and changes in the microstructure of the matrix. The joints are fractured at the diffusion zone, and the fracture exhibits a typical brittle characteristic. The present study successfully confirmed that by avoiding dendritic microstructure, as often resulted from the fusion welding, high joining quality components obtained in the semi-solid state. These results can be obtained without complex or additional apparatuses that are used in traditional joining process