Investigation On Adhesive Friction And Wear Behaviors Of 7075 Aluminum Alloy In Hot Stamping Process

The rapid growth of automobile ownership has put tremendous pressure on the environment and energy,so it is particularly important to promote the lightweight of automobiles.Aluminum alloy is an ideal lightweight material with excellent comprehensive performance,which can improve the performance of parts while reducing weight.The application of hot stamping process for heat-treatable aluminum alloy sheets has solved the sever defects like cracking and springback during room temperature,and promoted the application of aluminum alloy.At present,one of the key issues that restricting the promotion of the aluminum alloy hot stamping process is the severe friction problem.At elevated temperatures,the aluminum alloy is easy to adhere to the die surfaces.The material transferred from the aluminum alloy will form bonding points on the die surface,scratch the sheet surface,and cause severe galling.Therefore,this thesis takes 7075-T6 aluminum alloy sheets as the object,the friction behavior in the hot stamping process under different process parameters and die coatings were studied,the cumulative wear behavior of the friction pairs was explored,and the influence of COF and BHF on the formability of 7075 aluminum alloy complex components were studied by numerical simulation and forming experiments.The friction behavior of 7075 aluminum alloy sheets at elevated temperatures were studied by high-temperature friction experiments carried out on the self-made hightemperature friction tester.The aluminum alloy sheets have severe adhesive wear at elevated temperatures,and the maximum average friction coefficient was got when the sheet temperature is 350 ?.The sliding speed has no significant effect on the average friction coefficient.The normal pressure has a greater impact on the friction behavior,the average friction coefficient increases with the increasing normal pressure.The Merklein friction model was fitted and corrected according to the experimental results,which can reflect the friction behavior of 7075 aluminum alloy to a certain extent.The friction behavior of boriding treatment,ta-C coating,and WC-a-C:H coating with7075 aluminum alloy at elevated temperatures were studied.The results showed that the coatings all showed excellent lubricating effects at 300 ?.Among them,the samples with boriding treatment have the minimum average friction coefficient at 300 ?,and it shows the better anti-adhesion ability above 400 ?.The friction performance of the WC-a-C:H coating at 300 ? is more stable than the others.The cumulative wear behavior of the friction pairs was studied through repeated hightemperature friction experiments.The results showed that the 7075-aluminum alloy is very easy to adhere to the friction pair,the adhesive bonds grow sharply,and the growth rate of the lower friction pair is faster than the upper friction pair.The continuous accumulation of sticky matter has little effect on the average friction coefficient,but it will cause more serious scratches to the sheet.The results of numerical simulation and forming experiments of B-Pillar reinforced panel showed that the COF and BHF have a great influence on the formability of the components.The main reason is that the large COF and BHF will generate a large friction force and increase the flow resistance of the material flow.At the same time,due to the uneven contact between the sheet metal and the die,the uneven temperature field is generated,and the load-bearing capacity of the local material is reduced,which leads to rupture.With the decrease of the COF and the BHF,the cracking defects of the parts are reduced,but the lower BHF will cause wrinkle defects.