Research On Shaped Metal Deposition Of 2219 Aluminum Alloy By AC-TIG Welding

As one method of rapid prototyping, shaped metal deposition(SMD) by arc welding has the good features of low manufacturing cost, high efficiency, good controllability and metallurgical property, which has been paid more attention by many researchers recently. 2219 aluminum alloy is widely used in aerospace field because of its high strength, good corrosion resistance and weldability, etc. Research on the forming, microstructure and mechanical properties of shaped metal deposition of 2219 aluminum alloy by AC-TIG welding is carried out on this paper.In the beginning, samples of single channel with multi-layer are formed on substrates of different thickness with the same molding parameters. As a consequence,the thickness of substrate has no impact on the weld width of the stable region of sample. Based on this conclusion, samples built by quadratic general rotary unitized design method are taken advantage of to construct a predicting model aiming for the molding dimension of the sample’s stable region, which turns out that the predicting model has good prediction accuracy and prediction. The analysis of the impact on the weld width of the samples indicates that welding current, welding speed and inerpass temperature are the main factors. Additionally, welding current and inerpass temperature shows an interaction on the weld width. Three current change strategies are taken to keep deposited metal width stable, and the results show that the optimal control strategy of keeping deposited metal width stable on different substrate thickness is different,which reveals the variation that with the increase of substrate thickness, difference of heat dissipation between adjacent layers will increase too.The characteristics of typical microstructure of thin deposited aluminum samples is analyzed, from which we know that the difference of constitutional supercooling caused by changes of temperature gradient and crystallization rate in different regions of the sample is the main reason for the changes of micro-morphology. Four thin aluminum samples with same size are deposited using different parameters. The microstructure and mechanical properties are compared with each other. The results show that horizontal and vertical tensile strength has no anisotropy. The maximum tensile strength is 248 MPa, which is almost 60 percent of base metal. However, horizontal and vertical elongation has anisotropy, which depends on the microstructure and growth direction of grains. Microanalysis for fracture of horizontal and vertical tensile samples is carried out, and their fracture mode is the combination of transgranular fracture and intergranular fracture mode. The fracture surface has a large number of dimples, which is small but shallow. Furthermore, the morphology, distribution and formationmechanism of porosity is studied and some measures can be taken to control and reduce porosity.Optimal model of single layer with multi-channel weld spacing is analyzed and improved, which is proved to be precise and universally applicable. Then thick aluminum sample with different designed molding routes are deposited to study the influence of molding routes on forming, microstructure and mechanical properties of samples. Result shows that different molding routes and changes of heat dissipation caused by it is the main reason for the difference of macrostructure and microstructure.The mechanical properties of thick deposited aluminum samples are not only depended on heat input and heat dissipation conditions but also the microstructure and growth direction of grains. According to the dimples on fracture surface, we know the fracture mode of it is ductile fracture.