Study On Micropore Processing And Acoustic Properties Of Aluminum Foam

Foamed aluminum is a new type of material with a large number of pores distributed in aluminum-based alloys.It not only retains the electrical conductivity and high specific strength of metal materials,but also has the characteristics of light weight,sound absorption,energy absorption,vibration reduction and other porous materials.It has the characteristics of integration of structure and function,and has broad application prospects in submarine,armored vehicles and other national defense,high-speed rail,automobile and other transportation fields.The high-frequency sound absorption performance of foamed aluminum is good,but the low-frequency sound absorption performance is very poor,and the sound absorption frequency band is very narrow.The current research mainly optimizes the pore structure from the preparation method.A few scholars have studied the effect of mechanical perforation on the acoustic performance of foamed aluminum.However,due to the large processing aperture,the sound absorption potential of the tiny holes cannot be used,and the effect of processing technology on the acoustic performance of foamed aluminum is not paid attention to.Therefore,the paper based on the special machining technology,by optimizing the relevant technological parameters,different microporous structures on the surface of foam aluminum was processed,and the influence on the sound absorption properties of aluminum foam samples in the middle and low frequency(250Hz-2000Hz)was studied.Firstly,the high-speed electric spark drilling machine is used to process micropores on the surface of the foam aluminum.By analyzing the changing law of the sound absorption performance of different types of open cell aluminum foam and closed pore aluminum foams with different structural parameters before and after drilling to select more ideal test material.The results show that the sound absorption coefficient of perforated aluminum foam is reduced after drilling.The sound absorption coefficient of closed cell aluminum foam with different porosity and thickness is increased to varying degrees.When the thickness is constant,the sample with a porosity of 81.5% has the best sound absorption property;when the porosity is the same,The greater the thickness of the perforated sample,the better the sound absorption effect.Secondly,in order to further improve the processing accuracy and efficiency of microholes and reduce electrode loss as much as possible,through single factor experiments,the influence of peak current,pulse width and electrode diameter on aperture gap,processing time and electrode loss were studied separately.Researchs show that: smaller peak current and pulse width are beneficial to improve machining accuracy,but will reduce machining efficiency;when the electrical parameters are fixed(peak current 4A,pulse width 3 gears),as the electrode diameter increases,the aperture gap decreases,the machining accuracy is improved,and the electrode loss is reduced,but the machining time will be longer.Finally,different foamed aluminum sound-absorbing structures were designed and processed,and the influence of micropore structure,micropore distribution,cavity depth,and combined structure on the sound absorption peak,sound absorption coefficient and other indicators was studied.The results show that: the perforation aperture and perforation rate have the optimal range,too large or too small are not conducive to sound absorption;the perforation depth has a greater influence on the sound absorption coefficient,which increases with the increase of the perforation depth;the hole distribution method has little impact on the sound absorption performance.Among them,the conventional square distribution has a better sound absorption effect;with the increase of the depth of the back cavity,the absorption peak moves to the low frequency direction,and the peak value decreases gradually;the perforated samples with larger porosity and the sound absorption effect of the foam aluminum plate combination is better;placing the unperforated sample in front of the perforated sample can improve the sound absorption coefficient in the middle and low frequency bands;Proper combination of different types of punch aluminum foam samples can absorb almost all sound waves in the 1200Hz-2000 Hz frequency band.