Study On TiB₂/Al-Si Matrix Composites Fabricated By Wire And Arc Additive Manufacturing Based On CMT

In order to meet the production requirements of large and complex structural parts in aerospace and other fields,this research has realized the rapid prototyping of TiB₂/Al-Si composites using wire and arc additive manufacturing technology based on CMT(WAAM-CMT).This paper systematically studied the influence of CMT modes(CMT,CMT-ADV,CMT-P),heat input,travel speed and the flow rate of shielding gas on the weld morphology,weld size and porosity.It was discussed the solidification mechanism of WAAM-CMT and the effect of TiB₂ particles on the microstructures and mechanical properties of the printed samples.Besides,heat treatment which was suitable for WAAM-CMT printed samples was optimized and the strengthening mechanism of WAAM-CMT printed TiB₂/Al-Si composites was analyzed.Studies showed that different welding modes had little influence on the size of weld bead,but the porosity of the weld bead in CMT mode was much higher than that in the other two modes.CMT-ADV and CMT-P modes were more appropriate for the forming of TiB₂/AlSi7Mg0.6composites by WAAM-CMT technology.When adopting CMT-ADV mode,the flow rate of shielding gas had a small influence on the size of weld bead,which was affected by heat input and travel speed greatly.What's more,increasing the heat input and travel speed could reduce the porosity to some extent.In the process of WAAM-CMT printing,the welding current had better be controlled between 135A and 156A,the parameter range of travel speed ought to be between 12mm/s-13mm/s,and the flow rate of shielding gas should be 20L/min.The microstructures of the WAAM-CMT printed TiB₂/AlSi7Mg0.6composites were composed of primary?-Al and eutectic Al-Si,and the eutectic Si phase was distributed along the grain boundary with a strip-like or flaky-like shape.Compared with the secondary dendrite arm spacing of casting AlSi7Mg0.6 aluminum alloy(25?m),that of WAAM-CMT printed AlSi7Mg0.6 alloy was only about 8?m.In addition,the addition of TiB₂particles also played a role in grain refinement.The average grain size of WAAM-CMT printed TiB₂/AlSi7Mg0.6 composite was 28?m,which was also significantly smaller than that of the printed aluminum alloy(53.4?m).T6 heat treatment was suited to the microstructure optimization of WAAM-CMT printed samples,while direct aging treatment didn't significantly improve the properties of the materials.In addition,pre-aging could accelerate the speed of aging hardening.The optimal heat treatment process was 535°C/1h+120°C/1h+165°C/8h.The yield strength,tensile strength and elongation of TiB₂/AlSi7Mg0.6 composites made by WAAM-CMT technology could reach 102.97MPa,215.75MPa and 7.47%,respectively.After T6 heat treatment,the elastic modulus of the sample could be increased by 73.6%.The strengthening mechanism of WAAM-CMT printed TiB₂/AlSi7Mg0.6 composite is as follows.Fine grain strengthening caused by faster cooling rate and the addition of TiB₂ particles;Dispersion strengthening as a result of the existence of precipitation phase generated by T6 heat treatment;Solid solution strengthening of Si atoms due to solute interception effect and solution treatment;TiB₂ particles play the role of load reinforcement because of the load transfer mechanism.