| Nowadays, the application of aluminum alloys at elevated temperatures (250-350°C) has been raised due to the demand in automotive and aerospace industries. However, the rapid coarsening of precipitates in traditional precipitation-hardening aluminum alloys, such as 2xxx, 6xxx and 7xxx alloys results in a sharp decrease of elevated-temperature strengths. Therefore, developing a low-cost but thermally stable aluminum alloy is always a key concern in industries. Recently, the potential elevated-temperature applications of 3004 alloy has been investigated and found that the precipitation of dispersoids can remarkable improve the elevated-temperature strength and creep resistance, which can be thermally stable up to 300°C. However, the strength decreases with increasing temperature beyond 300°C. In order to further improve the elevated-temperature strength and retard the coarsening rate of dispersoids, Mo, as one of the transitional elements which have much lower diffusion rate has been added in 3004 alloy in present work to study the effects of Mo addition and heat treatment on properties of AA3004 alloys. A systematic study on properties of as-cast and heat-treated conditions was performed to fully investigate the characteristic of Mo addition in AA3004 alloys as well as its influence on the dispersoids precipitation behavior and strengths.;The results demonstrated that alpha-Al(Mn,Fe,Mo)Si dispersoids forms during the proper precipitation treatment both in interdenite and intradendrite zone, leading to a higher volume fraction of dispersoids and less dispersoid free zone (DFZ) compared with the base 3004 alloy. Therefore, the elevated-temperature properties, such as the yield strength and creep resistance at 300°C, have been further improved with the addition of Mo (~ 0.3 wt. %) after heat treatment. Besides, though elevated-temperature properties reduces with increasing temperature beyond 300°C, however, the decreasing rate is much lower than the base 3004 alloy benefited from the slower coarsening rate of alpha-Al(Mn,Fe,Mo)Si due to the low diffusion of Mo. In addition, alpha-Al(Mn,Fe,Mo)Si dispersoids is found to be thermally stable up to 350°C compared with 300°C in the base 3004 alloy, further widening the applications of 3004 alloys at elevated temperature. A preliminary study on the preheating treatment on improving the elevated-temperature properties also has been performed and the found the properties can be further improved by pretreated at 250°C for 24 hours.;With the addition of 0.3 wt. % Mo and treated after 250°C for 24 hours followed by peak precipitation treatment (375°C for 24-48 hours), the yield strength and creep resistance at 300°C can be further improved by 12% (from 78MP to 88MPa) and 53% (from 1.3x10-8s-1 to 6.1x10-9s-1 in minimum creep rate), respectively, compared with base 3004 alloy after peak precipitation treatment while the applicable temperature range has been extended to 350°C, providing the more promising potential of 3004 alloys for the elevated-temperature applications. |
