Study On Microstructure And Mechanical Properties Of The Liquid Forging 7055 Aluminum Alloy

The 7055 aluminum alloy having the highest strength and supper performance in 7XXX series aluminum alloy that belongings to ultra-high strength and toughness aluminum alloy group is widely used in aviation, aerospace, transportation and other industries for low density, high toughness, specific strength, low processing cost etc.Many domestic and international scholars and experts are therfore attracted to make their deep researches on preparation technology, aging, homogenization, alloying and other processing of 7055 aluminum alloy. And the remarkable progress of improving mechanical properties has been made.But along with science and technology development, the comprehensive performance of the 7055 aluminum alloy is demanded higher than ever before.The research on preparing 70055 aluminum alloy in method of liquid forging technology to further improve its performance is still a gap in domestic field. The conclusions of this research are as follows:(1)For low pressure liquid-forged part,the grain in bottom is the smallest because it at first solidified when liquid forging. With the increasing of upper apex pressure finally from liquid forging machine, the grain of liquid-forged part is crushed, which makes the grain size in upside is smaller than that in bottom.For the heat-treated liquid-forged part, the microstructure in each characteristic position is enhanced because of heat treatment processing, the more adequate solid solution to the matrix produces remarkable effect to advance strengthening.(2)The grain sizes which firstly decreases and then increases with increasing pressure at the same position of the samples that made in different pressures tend to be smaller. The microstructure and grain size of the heat-treated samples tends to be bigger, but the second phase of the precipitation makes a strengthening effect, the solid solution is effective, and the variation trend of grain size is the same as that of in non-heat treated state.(3)The high undercooling of pressure head in low liquid pressure makes the solidification rate of the upper surface accelerated,and the liquid pressure at a higher temperature brings about forging deformation in upper surface. In the bottom surface, the surface roughness decreases with increasing pressure, and then tends to be stable. In the end face, it increases with the increase of pressure but is stable.(4)The mechanical properties of heat-treated samples outperforms than that of liquid forged without heat treatment, and the improved range and proportion of the performance of hardness, tensile strength, bending strength on the condition of all pressures are basically tend to be same. The performance of impact toughness fluctuated greatly and increases to maximum value in pressure 75MPa. After heat treatment, the fracture toughness of the material increases with the liquid forging pressure.For the heat treated samples, the optimum performance liquid pressure of tensile strength, bending strength and hardness are 125MPa,125MPa and 75MPa,and for the non-heat-treated simples, the optimum pressures are 100MPa,125MPa and 100MPa.The KIC performance increased under low pressure but keep stable when pressure is greater than 50MPa.