Investigation On The Processing And Mechanism Of Friction Stir Additive Manufacturing Of High Strength Aluminum Alloy

With the increasing requirement of lightweight in many manufacturing industries,the application of aluminum alloy material is more and more extensive.For aluminum components fabricated by fusion based additive manufacturing process,the major concerns include porosity,coarse grains and poor mechanical properties.Friction stir additive manufacturing(FSAM),as a new solid-state additive manufacturing technique based on friction stir welding(FSW),raises the possibility of fabricating large-scale aluminum components.Currently,the studies related to FSAM technology are extremely limited.In this paper,the special forming tool and fixture are designed for FSAM of 2024 high strength aluminum alloy.The influence of process parameters on forming quality,the forming characteristic,and the mechanical properties of FSAM samples are mainly investigated.We mainly study the following contents:Firstly,the forming principle of FSAM was studied in this article.And the defect types and defects formation mechanism in the forming process were analyzed.A concrete method to realize FSAM was put forward,and the forming process of this method was investigated in detail.Then,the influence of each parameter on the forming was analyzed by changing the single parameter.The results indicated that the influence of traverse speed v and rotation speed n on the forming quality is prominent,but the plunge depth h has little influence on the forming quality.Tilt angle has a certain positive effect on the defects elimination,and two-pass processing is found to be able to replace the tilt angle and ensure defect-free forming.The ideal parameters with traverse speed of 300 mm/min,rotation rate of 1000 rpm and plunge depth of 0.2 mm were optimized after lots of experiments.Finally,single-track,multi-track and multi-layer defect-free samples were successfully fabricated by the application of two-pass processing at appropriate parameters.These defect-free FSAM fabricated samples are cross-sectioned to observe the microstructure by optical microscope.Ultrafine equiaxed grains with the diameter about 9.4 ?m are obtained in the stirred zone,which is far smaller than the substrate of about 150 ?m.The test results of mechanical properties show that there are some differences in different directions,the mechanical properties parallel to the forming direction are better than that perpendicular to the forming direction.The elongation ratios of parallel and vertical forming direction come to 31.05% and 25.75%,which are 2.14 times and 1.77 times of the base material.