| Considering the development of 7xxx series ultra high strength aluminum alloys in our country, the strengthening of aluminum alloys was studied. With the help of OM, SEM and TEM etc., the effects of compositions and heat treatment on the alloys microstructure and mechanical properties, such as σ b, σ 0.2 and 5 under room temperature, were studied systematically. The mechanism of above effects was analyzed. Results of the study are as follows:1. In this experiment, the higher the content of (Zn+Mg)m, the higher the strength of aluminum alloy. When (Zn+Mg)m and (Zn/Mg)m are 10.13% and 4.99 respectively, 5σ alloy obtains the optimum comprehensive mechanical properties. The σb, σ0.2 , of 5σ alloy are 618.9MPa, 593.5MPa and 14.3% respectively.An increase in the concentration of (Zn+Mg)m above 11.52% will lead to the decrease of strength and elongation.2. In single aging treatment of alloy, the increase of strength is accompanied with the decrease in ductility. In the condition of T6 (130 ℃X22h), compared with 7050-T6, the o b, o 0 2, 8 are increase by 11.3%, 18.2% and 11.5% respectively.3. In dual aging, the effect of the second step aging temperature on the mechanical properties is more obvious than that of other factors. After dual aging , compared with 7050 thick plate , 5σ alloy properties are following : on the state of T76(125℃X9h+160℃X6h), ob increase by 8.3%, o02 increase by 14.6%, 5 decrease by 13%; on the state of T74(125℃X6h+180℃ X12h), σb increase by 11.9%, o 0.2 increase by 23.1%, 8 increase by 11.8%; on the state of T73(125℃ X 3h+170℃ X 18h), o b increase by 14.1%, σ 0.2 increase by 30.1%, 6 is equal.4. In RRA, when retrogression temperature is 216℃, and time is 300s , 5σ alloy's σb, σ 02 decrease by 10.2%, 12.6% respectively and elongation increase by 18.5%. when retrogression time is 600s σ b, σ 0.2 ,8 decrease by 16.3%, 20.2% , 12.4% respectively. |
PDF Full Text Request