Research On Hot Stamping Process Of 7075 Aluminum Alloy

In recent years,in response to the energy-saving and emission-reduction policies issued by the state,more and more lightweight aluminum alloy materials have been applied to automobile manufacturing,thus reducing the weight of automobiles and the emission of harmful gases.Compared with other series of aluminum alloys,7000 series aluminum alloys have obvious advantages in high specific strength and corrosion resistance compared with other alloys,and are ideal lightweight materials for automobiles.7000 series aluminum alloys usually adopt hot forming process.The hot stamping forming process parameters have an important influence on the mechanical properties of the final aluminum alloy.How do these process parameters such as solution time,transfer time,mold pressure and subsequent aging treatment affect the aluminum alloy.The mechanical properties are the object we need to focus on.In order to determine the best process parameters for hot stamping of 7075 aluminum alloy,the effects of different solution time and transfer time on the properties of aluminum alloy were analyzed.The cooling rate of the aluminum alloy sheet corresponding to different mold contact pressures and the effect of different cooling rates on the properties of the alloy were determined by experiments.In order to shorten the aging time,try to use the aging treatment method of pre-aging combined with baking treatment to replace the conventional aging treatment method.The 7075 aluminum alloy was processed into U-shaped parts using the determined process parameters,the forming quality of the U-shaped parts was investigated,the springback and hardness of the parts were measured,and the contribution value of the alloy strength under the two aging processes was analyzed.The main research conclusions are as follows:1 Comparing the hardness change of 7075 aluminum alloy with different solution time after natural aging time and the conductivity change of quenched alloy at the solution temperature of 475℃,the effective solution time is determined to be 8min.Comparing the mechanical properties of aluminum alloy after quenching with 6s and 15 s transfer time,it is determined that the appropriate transfer time should be less than 6s and not more than 15 s.The experiment obtained the cooling rate of aluminum alloy corresponding to different mold pressures,measured the strength and microstructure changes of 7075 aluminum alloy with different cooling rates after aging at 120℃/24 h,and determined the optimal mold contact pressure to be 30 MPa,corresponding to the cooling rate of 7075 aluminum alloy is60°C/s.2 The new aging treatment method using pre-aging combined with baking paint treatment attempts to replace the conventional T6 aging method.The pre-aging temperature is selected within the range of the T6 aging temperature of 120 °C and the dissolution temperature of the strengthening phase η’ phase in 7075 aluminum alloys at 220 °C,and the measurement is different.The hardness and yield strength of 7075 aluminum alloy under pre-aging conditions before and after baking paint treatment,the hardness value of 7075 aluminum alloy under 160℃/30 min pre-aging conditions after baking paint treatment,the maximum increase in hardness is 24 HV,and the yield strength reaches 485 MPa.About 92%of the T6 state aluminum alloy,the elongation is 11.2%.The number and proportion of transgranular fractured dimples in the fracture of alloy tensile parts are the highest compared with other alloys under pre-aging conditions.3 The 7075 aluminum alloy is processed into U-shaped parts using the determined hot stamping process parameters,and the feasibility of the process parameters is verified by analyzing the mechanical properties and formability of the parts.There is no obvious difference in the hardness of different positions of the U-shaped piece,the thickness is uniform,and the surface has no obvious defects and no wrinkles.Using Geomagic control software to analyze the U-shaped parts after forming,the average deviations of the U-shaped parts under the two aging paths are 0.186 mm and 0.195 mm respectively,which proves that the shape of the U-shaped parts is consistent with the mold,the forming effect is good,and the process parameters are acceptable.Practical.4The contribution value of 7075 aluminum alloy yield strength under two different aging paths is analyzed by microscopic characterization.The results show that the yield strength of 7075 aluminum alloy in HFQ+PA+PB state can reach about 90% of the conventional method HFQ+120℃/24 h.The yield strength contribution value of the two is analyzed,and the Orowan strengthening value of the former is 382 MPa smaller than that of the latter,which is 411 MPa,which is the main reason for the difference between the two.