| With the tightening of “fuel consumption” regulations and taking into account the rigorous demands of people on the cruising range of new energy vehicles,combined with the high goal of setting the aluminum content for bicycles in the“Energy-saving and New Energy Vehicle Technology Roadmap”,the steel body is The introduction of lightweight aluminum alloy materials has become the most reasonable and implemented solution for the current car companies.The implementation of the plan puts forward urgent engineering requirements and major challenges for the connection technology of steel and aluminum dissimilar materials.Because of the low electrical resistivity,high thermal conductivity,and high reflectivity of aluminum alloys,conventional steel body forming methods such as spot welding and laser tailor welding are difficult to make good connections between steel and aluminum dissimilar materials.The self-piercing riveting process is not sensitive to the physical properties of the material,and there is no heat input during the forming process.It is suitable for the connection of dissimilar metals of aluminum and steel,and has been applied in the body sheet metal parts by being combined with glue.However,considering the complex materials used in bodywork,the variety of riveting tools,the low strength of single-process self-piercing riveted steel-aluminum joints,and the need for solidification when plastic riveting is compounded,it is explored that between the steel riveting process and the mechanical properties of joints.The universal relationship has important implications for promoting the application of aluminum alloy in the body.This article aims at the practical problem of the low connection strength when the anti-collision beam assembly of HC340 LA and 6061-T6 is prepared for a certain vehicle model.Through the self-piercing riveting of different brands of steel and aluminum,the combination method,plate thickness,and workpiece material are studied respectively.The effect of process factors such as joint heat treatment(simulating car body baking process)and rivet groove(opening hole)on the mechanical properties of joints is as follows:(1)Firstly,according to the material and thickness of the workpiece,determine the reasonable matching relationship between rivet specifications,die and sheet thickness,and combination methods,and develop a lap joint scheme.After passing multiple trial rigging passes,the steel aluminum self-piercing riveting is obtained.Excellent process parameters.(2)Study on the effect of plate assembly method,workpiece thickness and workpiece material on mechanical properties of steel-aluminum dissimilar metal self-piercing riveting lap joints found that 1)whether Q235,DX51 steel and 5083 aluminum alloy are used for riveting or HC340 LA and 6061-T6 are selected aluminum alloy is riveted.When aluminum alloy is used as the lower layer plate,the joint generally has higher strength and failure displacement,which is the same as the conclusion of most literatures;2)When HC340 LA is used as the upper plate to overlap 6061-T6 aluminum alloy,the lower layer of aluminum The thicker the alloy plate,the greater the joint failure load and the greater the displacement of failure.3)The same kind of combination and thickness,HC340 LA steel plate /6061-T6 aluminum alloy plate joint strength than the Q235,DX51 galvanized sheet / 5083 aluminum alloy joints.(3)Taking into account the paint-bake operations in the vehicle body manufacturing process,the joints were heat treated at 170°C×20min and170°C×480min to simulate the baking conditions and analyze the time-dependent changes of the joints during the baking process.The results showed that No matter which material is selected,the heat treatment will not reduce the mechanicalproperties of the joint,confirming the process stability and performance consistency of self-piercing riveted steel and aluminum joints in the bodywork.Among them,the heat-treated 6061-T6 aluminum alloy plate/HC340 LA steel plate joint strength did not change much,but the shock absorbing capacity improved;the 5083 aluminum alloy/Q235 galvanized steel plate and the 5083 aluminum alloy/DX51 galvanized steel plate joints were significantly improved in their strength and plasticity after heat treatment.(4)Based on the analysis of the interface structure of the joints,the rivets are grooved to improve the opening behavior of the rivets in the lower plate during punching and riveting.The “trumpet” formed by opening the notches in the lower plate is beneficial to improve the work piece.The "retraction resistance" of the rivet when subjected to an external load increases the tensile shear load of the joint.The results confirmed that the grooving treatment can improve the tensile shear load of the joint,and the linear relationship between the depth of the notch and the tension and shear load is linear,the depth of the notch increases,the tensile shear load increases,but after the notch exceeds a certain depth,the shear The load decreases rapidly until it reaches the same level as the parent sample.It can be inferred that there is a critical value for the notch.For 2.0mm-HC340LA/2.0mm-6061 fittings,the rivet notch threshold is 1.2mm,corresponding to the maximum tensile shear load 5.045 kN,so the slotting treatment increased 11% of the tensile shear load has a positive effect on the solution to the problem of the lower connection strength in the front;on the other hand,the slotting treatment leads to a significant reduction in the failure displacement,which is due to the upper plate due to the notch during punching and riveting.There is a direct relationship between the resulting "meat" being squeezed into the joint.The research on the internal relationship between the steel aluminum self-piercing riveting process and the mechanical properties of the joints is of great value for further improving the joint strength through process optimization,and has a positive effect on promoting the application of aluminum alloy materials in the steel body. |
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