A Comparative Study on the Microstructures and Mechanical Properties of Al-10Si-0.5Mg Alloys Prepared under Different Conditions

Fabrication condition greatly influences the microstructures and properties of Al alloys. However, most of the available reports focus on a single fabrication technique, indicating there is still a lack of systematic comparisons among wider ranges of fabrication methods. In this paper, with conventional casting (via sand/Fe/Cu mold) and additive manufacturing (AM, via selective laser melting, SLM) methods, the effects of cooling rate (Ṫ) on the microstructures and mechanical properties of hypoeutectic Al-10Si-0.5Mg alloy are systematically investigated. The results show that with increasing cooling rate from sand-mold condition to SLM condition, the grain size (d) is continuously refined from ~3522 ± 668 μm to ~10 μm, and the grain morphology is gradually refined from coarse dendrites to a mixed grain structure composed of columnar plus fine grains (~10 μm). The eutectic Si particles are effectively refined from blocky shape under sand/Fe-mold conditions to needle-like under Cu-mold conditions, and finally to fine fibrous network under SLM condition. The tensile yield strength and elongation is greatly improved from 125 ± 5 MPa (sand-mold) to 262 ± 3 MPa (SLM) and from 0.8 ± 0.2% (sand-mold) to 4.0 ± 0.2% (SLM), respectively. The strengthening mechanism is discussed, which is mainly ascribed to the continuous refinement of grains and Si particles and an increase in super-saturation of Al matrix with increasing cooling rate.

Multi-objective optimization of alloying elements to enhance the wear resistance and impact strength of HCCI produced by furan sand mold

High Chromium White Cast Iron (HCWCI) plays a major role in manufacturing of wear-resistant components. Due to unique wear resistance property, attribution to the additions of carbide forming elements, they have been used for mill liner applications. By varying the wt% of alloying elements such as Cr, Ti, and Mo, the wear resistance and impact strength of High Chromium Cast Iron (HCCI) can be increased. To enhance the wear resistance property according to Central Composite Design (CCD), 16 samples were fabricated by varying the wt% of alloying elements. To fabricate the samples, furan sand molds were prepared and used for the further casting process. The properties of Furan sand mold enhance the mechanical properties and reduce the mold rejection rate, production time, etc. To attain the optimum Wear Rate (WR) and Impact Strength (IS) value without dominance, optimization techniques such as Response Surface Methodological (RSM) and Particle swarm optimization (PSO) are employed to solve the multi-objective problem. The RSM and PSO predicted optimum solutions are compared by using the Weighted Aggregated Sum Product Assessment (WASPAS) ranking method. The WASPAS result revealed that when compared to the RSM result, the PSO predicted optimal wt% of chemical composition (22 wt % Cr, 3 wt % Ti, and 2.99 wt % Mo) gives the optimum WR value (53 mm3/min) and IS value (3.77 J). To validate the PSO result, experiments were carried out for the predicted wt% of alloying elements and tested. The difference between the PSO predicted result and experimental result is less than 5% error which clearly shows that PSO is an effective method to solve the multi-objective problem.

EFFECT OF COOLING RATE ON MICROSTRUCTURE AND HARDNESS IN GRAY CAST IRON CASTING PROCESS

This study aims to investigate the thermal conditions of the molds, changes in microstructure and hardness of casting products using sand mold and permanent mold. The use of sand mold and permanent mold results in different cooling rates. Thermal analysis was performed using a thermocouple to obtain a temperature versus time curve. Metallographic observations were carried out using a Scanning Electron Microscope equipped with Energy-Dispersive X-ray Spectroscopy. The Vickers hardness test was carried out in three areas with different thicknesses. The results showed a constant temperature at 691 oC where the eutectoid phase reaction occurred. Testing with sand mold showed that cast iron with flake graphite was finer and spreader than graphite in cast iron produced by permanent mold. Meanwhile, gray cast iron from a casting process with a permanent mold has a higher hardness than gray cast iron from a casting process using a sand mold.

COMPUTER SIMULATION OF FILLING SAND MOLD PROCESS WITH MELT FOR BLANKS OF STANDARD TENSILE SAMPLES OF CAST IRON PRODUCTION

Visualization of the mold filling process in the environment of the LVMFlow software complex made it possible to identify the characteristic features of filling sand-shaped grey cast iron with melt to obtain samples for testing mechanical properties.

Microstructure and elevated temperature mechanical properties of Mg-6Gd-3Y-0.5Zr alloy cast by PEP–SET sand mold

The present work cast a complex Mg-6Gd-3Y-0.5Zr alloy component in a polybenzylic ether phenolic resin (PEP-SET) sand mold using by differential pressure casting. Microstructural characterization was carried out on the castings in the states of as-cast, solution treatment and aging treatment. Their mechanical properties were examined at elevated temperatures. The studied Mg alloy showed noticeably high tensile strengths up to 473 K, followed by a significant decrease with further increasing the testing temperatures. Its mechanical properties at elevated temperatures were compared with those of WE43 alloy fabricated under identical casting conditions.