Evaluation of the microstructure, secondary dendrite arm spacing, and mechanical properties of Al–Si alloy castings made in sand and Fe–Cr slag molds

The microstructure and mechanical properties of as-cast A356（Al–Si） alloy castings were investigated. A356 alloy was cast into three different molds composed of sand, ferrochrome（Fe–Cr） slag, and a mixture of sand and Fe–Cr. A sodium silicate–CO_2 process was used to make the necessary molds. Cylindrical-shaped castings were prepared. Cast products with no porosity and a good surface finish were achieved in all of the molds. These castings were evaluated for their metallography, secondary dendrite arm spacing（SDAS）, and mechanical properties, including hardness, compression, tensile, and impact properties. Furthermore, the tensile and impact samples were analyzed by fractography. The results show that faster heat transfer in the Fe–Cr slag molds than in either the silica sand or mixed molds led to lower SDAS values with a refined microstructure in the products cast in Fe–Cr slag molds. Consistent and enhanced mechanical properties were observed in the slag mold products than in the castings obtained from either sand or mixed molds. The fracture surface of the slag mold castings shows a dimple fracture morphology with a transgranular fracture nature. However, the fracture surfaces of the sand mold castings display brittle fracture. In conclusion, products cast in Fe–Cr slag molds exhibit an improved surface finish and enhanced mechanical properties compared to those of products cast in sand and mixed molds.

Optimization and experimental analysis of sweet potato ship-shaped transplanting trajectory using particle swarm algorithm

The mechanization of ship-shaped transplanting is currently an urgent problem that should be solved.The movement trajectory of the transplanting mechanism is the key technology to perform ship-shaped transplanting.In this study,a ship-shaped transplanting trajectory was built and a mathematical model of a four-link transplanting mechanism was developed based on the requirements of the sweet potato transplanting agronomic technology.The particle swarm optimization algorithm was used,with the length of the four-bar mechanism and the installation angle of the fixed bar serving as the variables to optimize.The objective was to minimize the deviation of the ship-shaped transplanting trajectory,yielding an iterative optimization solution.The MATLAB simulation results showed that the penalty factors of different proportions in the adaptive particle swarm optimization algorithm affected the transplanting trajectory.The optimal penalty factor parameters areα=0.6,β=0.4.They ensure that the transplanting trajectory fulfills the agronomic requirements,and limit the deviation in the return trajectory of the mechanism.The sizes of the optimized four-bar mechanism were 110,312,245,160,360,and,160 mm.The determined installation angle was 100°.The results of the field experiments demonstrated that the optimized four-bar transplanting mechanism can better fulfill the agronomic technical requirements of sweet potato ship-shaped transplanting.For a transplanting speed of 0.2 m/s,the average qualified rates of insertion depth,insertion length,and tail height were equal to 94.00%,93.83%,and 91.67%.The results obtained in this study provide a theoretical basis and technical support for studying and developing sweet potato ship-shaped transplanting machinery.