Microstructural coarsening of 7005 aluminum alloy semisolid billets with high solid fraction

作者：Jiang Jufu^*; Wang Ying; Atkinson H V

来源：Materials Characterization, 2014, 90: 52-61.

DOI：10.1016/j.matchar.2014.01.017

• 7005 aluminum alloy
• Microstructural evolution
• RAP process
• SIMA process
• Semisolid processing

In the present study, 7005 aluminum alloy billets were supplied in the warm extruded and T6 heat treated state. They were then reheated to the semisolid state and the microstructural evolution and coarsening investigated. This is necessary groundwork if the billets are to be formed to shape by semisolid processing, an innovative manufacturing route which has recently gained wide use for a range of aluminum alloys but which has not yet been applied to 7005. The results showed that the average spheroid size, liquid film thickness and liquid fraction of 7005 aluminum alloy increased with increase in soaking time. Intragranular liquid droplets were present in solid grains, and coarsened with increase in soaking time and isothermal temperature. The roundness of globules of solid in the semisolid state at 600 degrees C-615 degrees C was in the range of 1.5 to 2.0 after soaking for periods up to 12 mm at 620 degrees C, but for times greater than 15 min was more than 2, which is unlikely to be suitable for the semi-solid forming process, where smooth flow is required and therefore relatively round globules. When the isothermal temperatures were 600 degrees C, 610 degrees C, 615 degrees C and 620 degrees C, the coarsening rates were 542 mu m(3) s(-1), 606 mu m(3) s(-1), 683 mu m(3) s(-1) and 688 mu m(3) s(-1), respectively. The coarsening rate K increased with the increase of isothermal temperature. These values place this alloy on the dividing line between typical coarsening rates for normally cast alloys and typical coarsening rates for normally wrought alloys. This is attributed to the fact that the alloy has a relatively simple precipitation hardening system in comparison with other 7xxx alloys and the hardening precipitate (MgZn2) melts below the temperature the experiments have been carried out at, hence preventing the precipitates inhibiting liquid film migration and diffusion along narrow liquid films at spheroid boundaries. Coarsening tends to occur via Ostwald ripening and coalescence, but Ostwald ripening plays an increasing role with the increase of isothermal temperature.

• 出版日期2014-4
• 单位哈尔滨工业大学