Study On Refinement Mechanism And Strength-Toughness Mechanism Of Additive Manufacturing Al-Mg Alloy

Aluminum alloys have excellent advantages,such as low density,high specific strength,good ductility,and resistance to corrosion.It has been found that widespread application in aviation,aerospace,rail transit,ships,automobiles,and other industries.Additive manufacturing is an emerging technology for manufacturing solid parts by layer-by-layer stacking based on CAD/CAM digital model design.This method has the advantages of rapid and efficient forming,arbitrary forming,and material saving.With the continual innovation of sophisticated technology in the aerospace,defense,and military industries,as well as the further shortening of the structural component development cycle,high precision size and complicated shape have become the development direction of aluminum alloy structural parts.Because of its low manufacturing cost,high production efficiency,and broad application range,the wire and arc additive manufacturing aluminum alloy technique has become one of the research hotspots.The effects of nano Ti C/Ti refiner on the microstructure and properties of additive parts were studied in this paper by adding different amounts of nano Ti C/Ti refiner under MIG and CMT conditions,and the refinement mechanism,as well as the strength and toughness mechanism of nano Ti C/Ti on Al-Mg alloy,were thoroughly analyzed.Following that,the refining effect of Al-Ti-C and Al-Ti-B master alloys blended in a specific proportion on as-cast 5356 alloy was investigated further,providing a foundation for the following preparation of modified welding wire.The effects of process parameters and nano Ti C/Ti refiner on MIG WAAM of Al-Mg alloy were studied.The results show that the appearance and metallurgical quality of the additive parts are good and the coarse grains and columnar grains disappear and the overall grains are relatively small and uniform when the tightness of the wire plate is 2,the welding speed is 36 cm/min,the welding current is 65 A,and the interlayer waiting time is 150 s.At present,the average grain size is about 52.90μm and the tensile strength is 185.7 MPa and the hardness is 65.2 HV.When 0.6wt.%nano Ti C/Ti refiner is added,the average grain size of the sample is the smallest,which is reduced to 35.00μm from no refiner,and the decrease ratio is about 34%.The tensile strength increased to 211.8MPa and the hardness increased to 83.6 HV.Nano Ti C particles can be used as heterogeneous nucleation sites to inhibit grain growth and improve nucleation rate.At the same time,nano Ti C particles are adsorbed on the solid-liquid interface,which limits the grain growth and also inhibits the nucleation.Furthermore,the effect of a nano Ti C/Ti refiner on the Al-Mg alloy produced by CMT WAAM was examined.The results show that the grain refinement effect of Al-Mg alloy with 0.6wt.%nano Ti C/Ti grain refiner is the best.The average grain size of the alloy on the yz plane decreases from 53.06μm to 25.32μm,and the decrease ratio is about 52%.The xy plane decreases from 52.00μm to 25.80μm,and the decrease ratio is about 50%.When 0.6 wt.%nano Ti C/Ti grain refiner is added,the tensile strength of CMT arc additive manufacturing is 257.6 MPa,and the microhardness is 98.5 HV.The results show that both MIG and CMT can prepare Al-Mg alloy additive straight arm wall with good quality,and the microstructure and mechanical properties of the alloy are greatly improved after refining.The proportion of alloy grain refinement and mechanical properties improvement of CMT additive parts is larger than that of MIG process.Al-Ti-B/Al-Ti-C medium alloy was added in advance to introduce Ti C and Ti B₂to manufacture 5356 Al-Mg modified welding wire in order to better streamline the process of adding refiner in the additive manufacturing process.The average grain size of Al-Mg alloy decreases from 336.10μm to 81.01μm when the addition of master alloy increases to 0.6 wt.%,and the decrease ratio is about 76%.The fine Ti C and Ti B₂particles introduced into the aluminum alloy melt act as the heterogeneous nucleation core ofα-Al phase during solidification,which promotes the heterogeneous nucleation ofα-Al and improves the nucleation efficiency.The microhardness and tensile strength of the alloy with 0.6 wt.%master alloy refiner are the highest,which are 82.6 HV and 221.3 MPa,which are 23.8%and 8.5%higher than those of the ingot without master alloy.