| dc.description.abstract | The effects of the alloy compositions, homogenization and re-heating temperatures on the extrudability and mechanical properties of 2024 and 7046 aluminum alloys were investigated.
In this study, the extrudability was evaluated with the maximum extrusion pressure and the surface quality of the extruded products. The mechanical properties were investigated using tensile, impact and hardness tests. Differential scanning calorimetry (DSC) in conjunction with transmission electron microscopy (TEM) were used to characterize the matrix precipitates of the alloys. The microstructural and fractured characterization were examined by optical and scanning electron microscopy (SEM).
For the 2024 aluminum alloy, the homogenization treatment with 520℃ for 10h can effectively eliminate the segregation and eutectic phase of the cast alloy. The degree of the solute supersaturation was increased with the reheating temperatures, but too high reheating temperature would also cause a higher susceptibility to hot cracking during extrusion. The 2024 alloy with high Cu and Mg contents revealed a considerately tensile strength, but the lowest impact toughness; In contrast, the alloy with low Cu and Mg contents revealed lower strength but higher impact toughness. The existence of eutectic phase was found to significantly influence the toughness property but slightly on the tensile strength.
For the 7046 aluminum alloy, the optimum homogenization treatment examined was 470℃ for 24h. The degree of the solute supersaturation of the alloy after extrusion was increased with increasing the homogenization and reheating temperatures. The results indicated that the extrudability was increased with extrusion temperature. Higher hardness values would be obtained by increasing homogenization and reheating temperatures, however, the tensile strength was opposite to the hardness measurements. This strength decay was primarily due to the coarsening of the recrystallized structure. Moreover, the mechanical properties were significantly affected by the variation of the magnesium content, but slightly affected by the zinc content. The 7046 alloy with low Mg content exhibited the lowest strength but highest impact toughness. | en_US |