Investigation Of Solidification Of Several Titanium,Aluminum Alloys And Aluminum Matrix Composite Under Microgravity

Additive manufacturing technology of metal material under microgravity has advantages of timely in-situ manufacturing parts urgently needed of spacecraft,producing large components on orbit and reducing firing costs.It will play an important role in human space industry.In the process of manufacturing in outer space,the melt solidified on the same material substrate under microgravity,and studies showed that microgravity environment has an important influence on the solidification of metal.In order to explore the specific influence of microgravity environment on the solidification process of the alternative materials,experiments of titanium alloy TC4,TC8,TC20 and aluminum alloy AI-5Si,Al-10Si and composite 7vol%TiB2/Al were carried out by partially melting method using 50m long drop tube.By comparing and analysing the gravity and microgravity results of various alloys and composite,the following conclusions are obtained:1.The solidification structure of three titanium alloys TC4.TC8 and TC20 is equiaxed polycrystalline structure.The equiaxed rate of the bottom grain is higher and the size is smaller,while the middle and upper grains are largerly elongated.By comparison,the proportion of larger grains in ?g sample is more than that in g sample,and the nucleation rate is lower than that of g sample.In addition,the difference between TC8 ?g and g sample in solidification structure is biggest,which is related to its slow solidification rate.Moreover,no matter there is gravity or microgravity,there is no macrosegregation in the direction of epitaxial growth.The solidification process of three kinds of titanium is mainly dominated by thermal diffusion,due to the fast solidification rate and the weak influence of convection.2.The solidification structure of Al-5Si alloy and Al-7Si alloy is composed of ?-A1 dendrite and interdendritic eutectic structure.And the eutectic percentage of the ?g sample is higher than that of the g sample for both alloys,and the difference will decrease with increasing solidification speed and Si content.The primary dendrite spacing of Al-5Si alloy's ?g sample is higher than that of g sample at different solidification rates,and the primary dendrite spacing of Al-7Si alloy's ?g sample is slightly higher than that of g sample.The second dendrite arm spacing of g sample of both Al-5Si alloy and Al-7Si alloy is higher than that of ?g sample,and increasing solidification speed will reduce this difference.Compared with ?g sample,the segregation of Si element in g sample of Al-5Si alloy is more serious.However the segregation of Si element in ?g sample of Al-7Si alloy is more serious,and increasing solidification speed will exacerbate the difference.The solidification process of both Al-5Si and Al-7Si alloy is mainly affected by the buoyancy convection.3.The solidification structure of 7vol%TiB2/Al composite consists.of Al dendrites and TiB2 particles aggregated in the branches.Compared to the g sample,the dendrites in ?g sample are more thicker.In the direction of the epitaxial growth of the remelting region,the TiB2 particles are in discharged state.In g sample,the number of particles at the bottom of the remelting zone is more than that of ?g sample.With the solidification process,the number of particles is less than that of ?g sample.Thesolidification process of 7vol%TiB2/Al composite is influenced by both the buoyant convection and the sedimentation effect.