Development Of Semi-solid Slurry Making Process And Equipment Of 7075 Aluminum Alloy

As a significant near net-shape forming method for the metallic materials,rheoforming has attracted increasing interest of scientists and engineers due to its short process,low cost and high performance of parts.A key success of rheoforming is having an efficient and powerful process to prepare semi-solid slurry.Owing to excellent mechanical properties,7075 aluminum alloy has been widely used in aerospace,automobile and other fields.Nevertheless,it is difficult for conventional plastic forming to produce parts with low cost and good mechanical properties while SSP is expected to grapple with this problem.It should be stated,however,that there is no rheoforming process to date by far can produce good semi-solid slurry with medium solid fraction for 7075 aluminum alloy,which limits its further application.In this paper,a novel slurry making process and equipment of 7075 aluminum alloy are developed.The main results are as follows:?1?The liquidus,solidus and liquid fraction vs.temperature curve of 7075aluminum alloy,which were compared with 319s aluminum alloy,were obtained by differential scanning calorimetry?DSC?under different kinetic conditions and numerical simulation.The semi-solid temperature interval increases with the increase of cooling rate.The solidification temperature range of 7075 aluminum alloy measured is more than 150?.However,the liquid fraction curve of 7075 aluminum alloy did not show the inflection point in the medium solid fraction range as 319s alloy did.In addition,when the liquid fraction is over 50%and the cooling rate is relatively small?1¹0?/min?,the sensitivity to temperature is almost greater than0.03?^-1.In the actual slurry making process,there is usually uneven temperature inside and outside the semi-solid slurry.The high sensitivity of liquid fraction to temperature aggravates the degree of uneven liquid fraction and makes the slurry properties uneven.This is the biggest problem in slurry making process of 7075aluminum alloy.?2?In order to grapple with the problem,the Enthalpy Compensation Process for preparing semi-solid slurry of 7075 aluminum alloy was developed.The temperature field of the semi-solid slurry prepared by Enthalpy Compensation Process was simulated by ANSYS Workbench software.The results indicate that the temperature difference in the slurry is always more than 60?without induction heating process while being reduced to 6.8?using Enthalpy Compensation Process.There is sufficient enthalpy compensation when the induction current density is 30×10⁶A/m²,the frequency is 10kHz,and the heating time is 40⁴5s.When the enthalpy compensation is enough,there will be an increase of temperature difference before the end of heating.?3?Based on the Enthalpy Compensation Process,a set of devices were designed and developed for Enthalpy Compensation Process,which chiefly consist of induction power supply,pressure converter cabinet,induction coil,crucible,temperature measuring frame and other components.Semi-solid slurry with uniform temperature and medium solid fraction can be prepared by Enthalpy Compensation Process with heating power of 13.5 kW and current frequency of 1 kHz as well as heating duration of 5s⁵0s.The temperature field is relatively uniform and the temperature of the slurry is 618.6±2.1?.The maximum temperature difference in the radial and vertical direction of the slurry is 1.4?and 2.4?,respectively.