| With recent development in the marine,pressure vessels,military,automotive and aerospace industries,Al-Mg alloys are widely used for large-scale structural components due to their low cost,good toughness,excellent corrosion resistance,and relatively high strength-to-weight ratio.Wire arc additive manufacturing technology has attracted more and more attention owing to its advantages such as high deposition efficiency,high material utilization,low material and equipment costs,and unlimited parts size.In this study,the TIG-MIG hybrid arc is used as the heat source.Since the substrate is not connected to the power supply,the arc heat is fully used for the melting of the wire,which is a composite heat source with low heat input and high deposition efficiency.Therefore,the TIG-MIG hybrid arc is used for 5356 aluminum alloy additive manufacturing and mathematical models between process parameters and additive geometry is established.Then,single-bead multi-layer aluminum alloy component is manufactured with optimized process parameters,and the effects of different locations and different heat treatment temperatures on the microstructure,mechanical properties,and heat dissipation performance of the aluminum alloy components are investigated.The result shows that,under the fixed additive manufacturing process parameters,the process parameters and geometry have the following characteristics: when the current is lower than 160 A or the additive speed is higher than 40cm/min,the weld bead appears discontinuous and serpentine;when the voltage is higher than 25 V,the weld bead is not shaped with a lot of splashes;when the tungsten-substrate height is higher than 14 mm,discontinuous particles appear;when the additive speed is lower than 10cm/min,the molten metal piles up,resulting in arc extinguishing,and the weld bead is unable to continue forming.Models between process parameters and additive geometry have higher levels of significance and fit.The effect of process parameters on the additive height is as follows: voltage>additive>velocity>current=tungsten-substrate height;the effect of process parameters on the additive width is as follows: voltage >current>tungsten-substrate height>additive velocity.The microstructure result shows that the as-deposited and heat-treated microstructures are mainly equiaxed grains and the equiaxed grains are in the order of bottom,middle,and top in descending order of size.With the increasing of the heat treatment temperature,the ? phase gradually dissolves into the ?-Al matrix and the grain boundary gradually becomes apparent.A large amount of ? phase precipitates between the layers.The ? phase dissolves into the ?-Al matrix,and mixing of fine equiaxed grains and columnar grains appears after undergoing heat treatment.The mechanical properties and scanning fractures indicate that the hardness of aluminum alloys on all conditions increases with increasing distance from the substrate.The hardness value at top region reaches the maximum and the hardness value fluctuates greatly during the process.The average hardness increases from 64.2 HV0.1 to 75.3 HV0.1 when heat treatment temperature rises.The average tensile strength of as-deposited aluminum alloy increases from 226 MPa to 269 MPa and the average elongation gradually decreases from 29.75% to 12.2% as the heat treatment temperature increases.The as-deposited and 350°C heat treated fractures exhibit typical ductile fractures.The fractures heat treated at 450°C exhibit quasi-cleavage fractures,and the fractures at 550°C exhibit brittle fractures.All fractures exhibit transgranular and intergranular mixed fracture modes.Heat dissipation performance test shows that the temperature distributions of the as-deposited aluminum alloy,the 350°C heat-treated aluminum alloy and the 450°C heat-treated aluminum alloy on different location are uniform and the cooling rates on different location are the same.The temperature distribution of the heat-treated aluminum alloy at 550 °C varies at different locations and the cooling rate varies.By comparing the average temperature of all regions of the aluminum alloy on all conditions,it can be found that when the heat treatment temperature is 350°C and 450°C,the cooling rate of the as-deposited aluminum alloy can be significantly improved.When the heat treatment is performed at 550°C,the cooling rate of the as-deposited aluminum alloy is dropped significantly. |
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