چكيده به لاتين
Semi solid processing is a relatively new technology that is used for metal forming in semi solid state. This process is different from conventional metal forming technologies in which solid or liquid metals are used as starting materials. The main difference between the semisolid processing and casting is the formation of non-dendritic structure in the semisolid mixture. Powder Tixoforging is one of the semisolid forming methods. In this process, various parameters, such as cold pressing pressures, heating time, ball-milling time, preheating temperature to the semisolid region, and tixoforging pressure affect the end result. Any change in these parameters may alter the structure. Therefore optimizing these parameters is necessary to achieve a material with the microstructure and suitable mechanical properties. In the present work, a (V) shaped sample was produced by the powder thixoforging method. The aluminum alloy 520 was used to make the (V) shaped sample. Also, for the first time, a powder thixoforging method was used to make a large dimensional (V) shaped and healthy sample (recycled powderfrom milling chips by mechanical grinding method).
The results showed that the cold pressing pressures, heating time, thixoforging temperature and ball-milling time affect the structure of the samples in the powder thixoforging process. The impact of temperature and time of ball milling on the microstructure and the hardness of the powder thixoforged sample was studied. The optimum values of the parameters of powder cold pressing pressures (600MPa), heating time (3h), tixoforging temperature (605 °C), and ball-milling time (35h) were obtained to achieve a uniform microstructure and high hardness specimen, and a suitable distribution of spherical particles. By studying the microstructure of the samples at temperatures of 580 °C, 595 °C and 605 °C it was found that the temperature affects the solid fraction. Hardness is increased by increasing the ball-milling time due to decrease in particle sizes. Finally, the simulation of the process was done by Deform-3D software. Comparing the simulation results with hardness showed that the strain had an effect on the hardness. increasing the strain from the edge to the center of the powder thixoforged sample resulted in the increase of the hardness.
