| Metal matrix syntactic foam is a porous composite material composed of metal matrix and hollow particle.It has many excellent properties,such as light weight,high specific strength and specific stiffness,high damping,high energy absorption,sound absorption,heat insulation,sound insulation and so on.Among them,because of the reinforcement effect of hollow bead,the metal matrix syntactic foam has higher energy absorption than traditional foam metal.It has broad application prospects in the fields of energy absorption and cushioning,anti-collision and vibration reduction,explosion-proof and anti-seismic automobile,public safety,aerospace,military equipment and ships.At present,scholars at home and abroad have made extensive basic research on the composition,preparation methods,properties and applications of metal matrix syntactic foams.However,there are few reports on the research of gravity infiltration technology for preparing metal matrix syntactic foam filled with large particle hollow microspheres.In this paper,Al-Si-Cu-Mg alloy was used as metal matrix,0.5-2 mm Al2O3hollow particles were used as filling materials,and the gravity infiltration method was used to synthesized Al-Matrix syntactic foam.The effect of hollow particle size,infiltration temperature and infiltration time on the quasi-static mechanical properties of Al-matrix syntactic foam was studied by orthogonal test.In addition,the effect of Ni alloying element and heat treatment process on microstructure,quasi-static compressive properties and energy absorption properties of the Al-matrix syntactic foams were investigated.The main results are as follows:?1?The effects of particle size,infiltration temperature and infiltration time on the microstructure,quasi-static compressive properties and energy absorption properties of Al-matrix syntactic foams were investigated by orthogonal experiments.The results showed that with the increase of the infiltration temperature and infiltration time,Al2Cu?Si?Q?Al-Si-Cu-Mg?phases coarsened in composite matrix,while the Al-Fe-Si phase grew into a needle-bar shape.Interface between hollow particles and metal matrix with the increase of the infiltration temperature and infiltration time,the shape of the interface changed from arc to broken line,and sphericial shell of hollow particles were seriously incomplete due to reaction.The results of calculation and range analysis show that the effects of various factors on the four energy absorption indices are as follows:compression strength,particle size>infiltration temperature>infiltration time;average platform stress,particle size>infiltration temperature>infiltration times;specific energy absorption,particle size>infiltration time>infiltration temperature;energy absorption efficiency,infiltration time>infiltration temperature>particle size;F test showed that the particle size had a significant effect on the specific energy absorption.The optimum gravity infiltration process is as follows:hollow microsphere particle size is 0.5-1 mm,infiltration temperature is 750?,infiltration time is 60 min.The compressive and energy absorbing properties of the Al-matrix syntactic foam obtained from this collocation are 77.4MPa in compression strength,77.3 MPa in average platform stress,27.6 kJ/kg in energy absorption capacity,63%in energy absorption efficiency.?2?On the basis of the above parameters optimization,the effects of Ni addition on the microstructure,compressive properties and energy absorption properties of the syntactic foam were investigated.It was found that with the increase of Ni addition,the Al3Ni strengthening phase was larger and the quantity increased,while the Al2Cu phase gradually decreased and the Al-Si-Fe phase decreased.The results of quasi-static compression test showed that the compressive strength of the syntactic foam was higher than that of without adding Ni,but the average platform stress decreased and the energy absorption decreased.The best compressive energy absorption performance was syntactic foam with 2 wt.%Ni.The platform stress and specific energy absorption were 71.1 MPa and 25 kJ/kg,respectively.The results show that the Al3Ni metal compounds formed by the added Ni increase the compressive strength of the matrix material,but increase the brittleness of the matrix material.After the compression yield,the crack propagation rate is fast,and the compression platform fluctuate and jitter,resulting in a decrease in compressive properties and energy absorption properties.?3?Normalizing and annealing treatment of Al-matrix syntactic foam were carried out.The results showed that the acicular Al-Fe-Si phase of the syntactic foam disappeared after normalizing,and the eutectic silicon morphology changed from long strip to uniformly distributed granule,while the fine Al2Cu phase re-precipitated and dispersed.With the prolongation of annealing time,the morphology and distribution of Si phase and Al2Cu phase in the samples annealed for 2h are the best.After heat treatment,the maximum compressive strength is 120.2 MPa,the average platform stress is 95.3 MPa,the energy absorption capacity is 61.9 MJ/m3,the specific energy absorption capacity is 33.5 kJ/kg,the energy absorption efficiency is 70.6%,which increase 55.3%?21.3%?23.3%?31.1%?12.1%,respectively,compared with the as-cast.The results indicate that the releasing of residual compressive stress and the improving of morphology and distribution of matrix strengthening phase after heat treatment result in improving the compressing and energy absorbing properties of the syntactic foams. |
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