| Al-Si alloys are widely used in engines,vehicle industry,aerospace and other fields due to their high specific strength,high wear resistance and corrosion resistance,and low coefficient of thermal expansion.It is a hot spot to further promote the research of Al-Si alloy deformed materials by micro-alloying in-situ self-precipitation of multi-grade alloy phase particles to improve the static strength,plasticity,toughness and fatigue properties of the alloy.Therefore,it is of great scientific significance and practical engineering application value to reveal the synergistic effect of nanometers,submicron and microns alloy phase particles on the static and dynamic fracture behavior of Al-Si alloy deformed materials.This paper is aimed at Al-5Si alloy by means of metallographic microscope,scanning electron microscope,transmission electron microscope,tensile test,fatigue test and other experimental methods.Nanometer Mg2Si particles are precipitated by Mg.The effects of Mg content on the microstructure,mechanical properties and fracture behavior of under-aging and peak-aging Al-5Si alloy sheets are systematically investigated.Optimize the optimum Mg content that is reasonably matched to micron Si particles.Accordingly,the submicron phase particles are further precipitated by Mn.The effect of Mn content on the microstructure,mechanical properties and fracture behavior of under-aging and peak-aging Al-5Si-0.8Mg alloy sheets is investigated systematically.Finally,the optimum Mg content and optimum Mn content for the best static and dynamic mechanical properties of Al-5Si alloy sheets are optimized.Furthermore,the static and dynamic fracture behaviors of nano-scale Mg2Si particles,submicron Mn phase particles and micro-scale Si particles multi-stage particle composite toughened Al-5Si alloy sheets are revealed.The main conclusions are as follows:(1)Adding Mg and Mn can refine the eutectic structure of Al-5Si alloy ingot,addition of Mg,the ingot grain size to be refined from 406 ?m to 286 ?m.As the Mg content continues to increase from 0.33%to 1.42%,there is no significant change in the grain size of the alloy ingot.However,the addition of Mn to the Al-5Si-0.8Mg alloy and the increase of Mn can coarsen the grain structure,the size from 288 ?m to 448 ?m.The addition of Mg transformed the AlFeSi phase in Al-5Si alloy ingot the into AlFeMgSi phase.By adding Mn to the Al-5Si-0.8Mg alloy,the needle-rod AlFeMgSi phase in the alloy ingot can be converted into the needle-rod AIFeMnSi phase.When the Mn content reaches 0.72%,a fishbone AlFeMnSi phase with a size of about 20 ?m appears in the alloy ingot.When the Mn content exceeds 1.09%,through L+Al6Mn??-Al+Al9(FeMn)4Si3,the alloy ingot forms block Al9(FeMn)4Si3 with a size of about 50 ?m.(2)When Mg is added and the Mg content is increased,the number of precipitated phase particles Mg2Si in the Al-5Si-(0.01-1.42)Mg alloy sheet after artificial aging treatment is increased.After the alloy sheet is quenched by 540?×1 h and then artificially aging at 170?,the strength of the alloy sheet increased rapidly with the addition of Mg,and then decreased slightly after the peak value.The elongation rate decreased rapidly and then almost unchanged.When aging at 170? for 1 h,Al-5.53Si-1.10Mg alloy sheet has the best comprehensive performance,and its yield strength,tensile strength and hardness are 173 MPa,266 MPa and 92 HV,compared with Al-5.57Si without Mg,the yield strength and tensile strength of the alloy sheet increased by 122 MPa,the hardness increased by 49 HV,and the elongation decreased from 28.4%to 20.0%.The Al-5.56Si-0.78Mg alloy sheet has the best comprehensive performance at 170? for 10 h,and its yield strength,tensile strength and hardness are 285 MPa,320 MPa and 112 HV,compared with Al-5.57Si without Mg,the yield strength,tensile strength and hardness of the alloy sheet increased by 230 MPa,175 MPa and 69 HV,while the elongation decreased from 27.9%to 11.9%.(3)After water quenching at 540? ×1h and artificial aging treatment at 170?,the fatigue properties of the alloy sheet increased first and then decreased with the increase of Mg content.When aging at 170? for 1 h and 10 h,the number of nanometer Mg2Si particles produced by Al-5Si-0.78Mg alloy sheet best matched the number of micron-sized Si particles in Al-5Si,showing good fatigue performance,and at 150 MPa and 175 MPa and R=0,the mean fatigue life is the highest,1.05×106 times and 1.08×106 times,which is much higher than that of Al-5.57 Si alloy sheet without Mg under the same conditions,whose mean fatigue life is 7.08×104 times and 4.60×104 times,respectively.(4)The optimum Mg content of the Al-5Si-(0.01-1.42)Mg alloy is optimized to be 0.8%.On the basis of this,Mn is added.With the increase of Mn content,the Al-5Si-0.8Mg-(0.01-1.97)Mn alloy sheet is quenched by 540?×1 h and then aging at 170?.The amount of submicron Mn-containing phase particles in the sheet increases.The strength and hardness of the sheet increased rapidly with the increase of Mn,and then slight decrease after the peak value.The elongation rate increased first and then decreased rapidly.The fatigue performance of the sheet showed a trend of increasing first and then decreasing.(5)Optimized the optimum Mn content in Al-5Si-0.8Mg-(0.01-1.97)Mn alloy sheet is 0.7%.The number of submicron Mn-containing phase particles produced is the best match with the number of micro-sized Si particles and nano-sized Mg2Si particles in Al-5Si-0.8Mg-(0.01-1.97)Mn.The yield strength,tensile strength and elongation of alloy sheets at 170? for 1 h are 230 MPa,326 MPa and 20.5%,respectively,and the yield strength and tensile strength of Al-5.64 si-0.78 Mg alloy sheet without Mn are increased by 72 MPa and 69 MPa respectively,and the elongation is equivalent.The average fatigue life of the alloy sheet under 170 MPa and R=0 conditions can reach 5.39×105 times,which is much higher than the average fatigue life of the Al-5.64Si-0.78Mg alloy sheet without Mn under the same conditions of 7.72×104 times.At 170? for 10 h,the yield strength,tensile strength and elongation of the alloy sheet are 321 MPa,362 MPa and 11.7%,respectively,and The yield strength and tensile strength of Al-5.64 si-0.78 Mg alloy sheet without Mn are increased by 36 MPa and 42 MPa respectively,and the elongation is equivalent.The average life of the alloy sheet under fatigue at 175 MPa and R=0 is 3.89×106 times,which is much higher than the average fatigue life of 1.05×106 times under the same conditions of Al-5.64Si-0.78Mg alloy sheet without Mn.(6)170?×1 h under-aging and 170?×10 h peak-aging Al-5Si-(0.01-1.42)Mg alloy sheet static tensile fracture main cracks bypass or pass through Si particles,170?×1h under-aging state and 170?×10 h peak-aging Al-5Si-0.8Mg-(0.01-1.97)Mn alloy sheet static tensile fracture main crack pass through Al9(FeMn)4Si3 phase.Fatigue crack growth of 170?×1 h under-aging Al-5Si-(0.01-1.42)Mg alloy sheet bypasses Si particles;fatigue crack growth of 170?×10 h peak-aging Al-5Si-(0.01-1.42)Mg alloy sheet can bypass or pass through Si particles.When the Mn content does not exceed 0.72%,the fatigue life of Al-5Si-0.8Mg-(0.01-1.97)Mn alloy sheet can be improved by submicron phase particles When the Mn content exceeds 1.09%,the Al9(FeMn)4Si3 phase in the Al-5Si-0.8Mg-(0.01-1.97)Mn alloy sheet promotes crack initiation. |
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