| Aluminium alloy honeycomb sandwich structure has the advantages of light weight,high stiffness,high specific strength and high specific energy absorption,and plays an important role in lightweight load-bearing structure and armor protection in aviation,aerospace,weapons,automobiles,rail transit and other fields.Aluminium alloy honeycomb core and the panel are usually connected and formed by gluing,brazing and other methods,which leads to the lack of overall comprehensive performance due to the low interface bonding strength,which limits its promotion and application in aerospace,weapons and military industry.As an efficient and energy-saving connection method,friction stir welded technology is based on the principle of plasticizing materials by using frictional heat,and realizing solid-phase connection through mixing and extrusion,which effectively improves the interfacial bonding strength,plastic toughness,fatigue resistance and other properties of materials.In this paper,the solid phase connection between the aluminium alloy honeycomb core and the panel is realized by friction stir welded,the interface state evaluation and macroscopic mechanical behavior of the aluminium alloy honeycomb sandwich structure based on friction stir welded are studied,and the relationship between the process parameters,interface bonding state(interface microstructure state,interface bonding strength),macroscopic mechanical behavior and failure mechanism of aluminium alloy honeycomb sandwich structure prepared by friction stir welded process is established,and the relevant research contents and conclusions are as follows:(1)The influence of friction stir welded and heat treatment technology on the microstructure evolution of 6061-T6 aluminium alloy T-shaped joint was studied,and the relationship between welding and heat treatment process parameters and interface microstructure state was established.The results show that the weld seam of 6061-T6 aluminium alloy T-shape joint is more than 80%,and it can reach 96% when the stirring needle is 1050 r/min and the welding speed is 100 mm/min.As the solution temperature increased from 505 ℃ to 564 ℃,the grain size grew from 189 μm to 318 μm.The orientation difference between grains is close to the free orientation difference,and there is no obvious preferential orientation.Circular or oval dimples of different shapes and sizes were observed in the T-shape joint fractures,and ductile fractures were the main ones.(2)The effects of welding and subsequent heat treatment process on the interfacial bonding strength and tensile failure mechanism of T-shape joint were analyzed,the constitutive model of T-shape joint and the relationship between process parameters and interface microstructure and bonding strength were established,and the optimal welding process parameters were optimized and determined.The results show that when the welding speed is 100mm/min,the interfacial bonding strength of friction stir welded 6061-T6 aluminium alloy T-shape joint along the rib plate and along the wall plate is higher,which is 53.98 MPa and 179.54 MPa,respectively.At the solution temperature of 565 ℃,the holding time of 4 h,the aging temperature of 180 ℃,and the holding time of 3 h,the interfacial bonding strength of the friction stir welded 6061-T6 aluminium alloy T-shape joint along the rib plate and along the wall plate was relatively high,which was 44.81 MPa and 183.79 MPa,respectively.(3)The friction stir welded aluminium alloy honeycomb sandwich structure was tested for the flat pressure behavior,the flat pressure performance of the square hollow section and the hexagonal hollow section honeycomb sandwich structure was evaluated,the finite element simulation model of the flat pressure sample was established,and the relationship between the geometric parameters and the flat pressure behavior was clarified based on the test and finite element simulation results.The results show that the finite element model can accurately predict the flat compression performance of friction stir welded 6061-T6 aluminium alloy honeycomb sandwich structure.(4)The lateral pressure behavior of friction stir welded aluminium alloy honeycomb sandwich structure was studied,the lateral pressure performance of the square honeycomb sandwich structure was evaluated,the finite element simulation model of the lateral pressure sample was established,and the relationship between geometric parameters and lateral pressure behavior was clarified based on the results of test and finite element simulation.The results show that with the increase of cell size,the ultimate load,inflection point and peak compressive strength of the aluminium alloy honeycomb sandwich structure decrease,and with the increase of the height of the honeycomb core,the ultimate load increases slightly,but the peak lateral compressive strength decreases significantly.At the same time,the increase in cell size and honeycomb core height leads to a decrease in the inflection point side compressive strength and peak side compressive strength.(5)The research on the three-point bending mechanical behavior of the friction stir welded aluminium alloy honeycomb sandwich structure was carried out,the bending performance of the square honeycomb sandwich structure was evaluated,the finite element simulation model of the bending sample was established,and the relationship between the geometric parameters and the three-point bending mechanical behavior was clarified based on the finite element simulation and test results.The results show that with the decrease of cell size,the failure mode of the honeycomb sandwich structure gradually transitions from global buckling to local buckling of the side wall of the honeycomb core,which makes the panel more prone to cracking and failure.Reducing the cell size or increasing the height of the honeycomb core can effectively enhance the bending capacity of the aluminium alloy honeycomb sandwich structure. |
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