Research On The Sound Absorption And Compression Properties Of A356 Aluminum Alloy/304 Stainless Steel Fiber Composite Foam

Sound-absorbing aluminum foam has excellent properties such as high toughness,high temperature resistance,non-hygroscopic deliquescence and recyclability,and has broad application prospects in the field of sound absorption and noise reduction.However,there are also problems of low sound absorption coefficient of large pore size（>1 mm）and single pore structure sound-absorbing foam aluminum,and low strength of high porosity sound-absorbing aluminum foam.Therefore,in this paper,the pore structure refinement and special treatment are used to improve the sound absorption performance of the sound absorbing foam aluminum,and the stainless steel fiber reinforcement and heat treatment are used to improve the mechanical properties of the sound absorbing foam aluminum.It lays the foundation for the development of high sound absorption and high strength sound absorbing composite foam.In this paper,a single and special pore structure of A356 aluminum alloy/304 stainless steel fiber composite foam with high porosity and pore size（<1mm）was prepared by seepage casting method.The sound absorption performance and compression performance of composite foam were studied.The results are as follows:（1）A single-porosity composite foam with a pore diameter of 0.21⁰.85mm and a porosity of 81⁸3%was prepared.The static flow resistivity,surface area and sound absorption performance of different pore size composite foams were studied.The results show that the smaller the pore size of the composite foam,the larger the static flow resistivity and specific surface area,and the better the sound absorption performance.The composite foam with a pore size of 0.21 mm has the best sound absorption performance,and the average sound absorption coefficient（800⁶300 Hz）is 0.84.The sound energy loss mechanism of single hole structure composite foam mainly depends on its static flow resistance.The greater the static flow resistance,the greater the friction and viscous resistance caused by sound waves,and the greater the acoustic energy loss,the better the sound absorption performance.（2）A layered periodic pore structure composite foam with pore size of 0.21⁰.85mm,porosity of 81⁸3%and cycle number of 1³ cycles was prepared.The average sound absorption coefficient of the layered periodic pore structure composite foam increases first and then decreases with the increase of the interlayer pore size difference.The optimal interlayer pore size difference is about 0.44mm.The larger the number of cycles,the higher the sound absorption performance of the composite foam.The optimal lamellar periodic pore structure is a three-cycle,six-layer（0.65+0.21+0.65+0.21+0.65+0.21）pore structure composite foam with an average sound absorption coefficient of 0.87.It is superior to a single-porosity composite foam with an average pore diameter of 0.45 mm and a minimum pore size of 0.21 mm,and the sound absorption coefficient of the low frequency region（800²500 Hz）and the sound absorption trough is significantly improved.（3）A layered gradient pore structure composite foam with a pore size of 0.21⁰.85mm,a porosity of 81⁸3%and a gradient layer of 3⁵ layers was prepared.The composite foam with layered gradient pore structure has the best sound absorption performance when the adjacent aperture difference is 0.1mm,the more the gradient layer,the better the sound absorption performance.The optimum average sound absorption coefficient of the layered gradient pore structure composite foam is 0.82.The sound absorption performance of the layered periodic pore structure composite foam is better than that of the layered gradient pore structure composite foam,mainly because the sound absorption coefficient of the low frequency band（800²500 Hz）and its absorption peak are improved.The sound absorption mechanism of the expanded chamber structure with special pore structure shows that the pore size is similar to that of the tube,and the sound wave propagates in different sections of the pipeline,resulting in the sudden change of acoustic impedance in the channel,the increase of acoustic energy loss and the increase of sound absorption.When the pore structure of the composite foam and its static flow resistance and expansion chamber structure theory are optimally matched,the acoustic wave loss is the largest and the sound absorption performance is the best.（4）Single hole structure composite foam and layered periodic pore structure composite foam increase the back cavity,the resonant absorption peak moves to the low frequency direction,the sound absorption coefficient of the low frequency area increases obviously,the average sound absorption coefficient is improved,and the best back cavity thickness is 10mm.The optimum sound absorption coefficient of single pore structure composite foam with 0.21mm diameter and three cycle 6 layer（0.65+0.21+0.65+0.21+0.65+0.21）pore structure composite foam is 0.87 and 0.89 respectively.（5）The compressive properties of a single pore structure of the composite foam showed that when the porosity of the composite foam was fixed to 81⁸3%,the fiber distribution increased from 0vol.%to 7.5vol.%.The fibers are distributed in the form of inlaid in the middle of the hole wall,connecting the hole and extending the end in the hole.Its yield strength and energy absorption value increased first and then decreased.The optimum fiber content was 5 vol.%,and the yield strength was 6.12 MPa.When the pore diameter of the composite foam is reduced from0.85 mm to 0.21 mm,the yield strength gradually increases from 6.01 MPa to 7.81 MPa,and the energy absorption capacity is also gradually increased.T6 heat treatment can refineα-Al grain and eutectic silicon transforms from dendrite to smaller ellipse or globule.The degree of homogenization of the structure increases and the enhanced phase Mg₂Si is produced.Compared with the non-heat treated composite foam,the yield strength is increased by 30³2%,and the energy absorption is also obviously improved.