Abstract: Friction rolling additive manufacturing (FRAM) is a solid-state additive manufacturing technology that plasticizes the feed and deposits a material using frictional heat generated by the tool head. The thermal efficiency of FRAM, which depends only on friction to generate heat, is low, and the thermal-accumulation effect of the deposition process must be addressed. An FRAM heat-balance-control method that combines plasma-arc preheating and instant water cooling (PC-FRAM) is devised in this study, and a temperature field featuring rapidly increasing and decreasing temperature is constructed around the tool head. Additionally, 2195-T87 Al-Li alloy is used as the feed material, and the effects of heating and cooling rates on the microstructure and mechanical properties are investigated. The results show that water cooling significantly improves heat accumulation during the deposition process. The cooling rate increases by 11.7 times, and the high-temperature residence time decreases by more than 50 %. The grain size of the PC-FRAM sample is the smallest, i.e., 3.77±1.03 µm, its dislocation density is the highest, and the number density of precipitates is the highest, the size of precipitates is the smallest, which shows the best precipitation-strengthening effect. The hardness test results are consistent with the precipitation distribution. The ultimate tensile strength, yield strength and elongation of the PC-FRAM samples are the highest (351±15.6 MPa, 251.3 ± 15.8 MPa and 16.25 %±1.25 %, respectively) among the samples investigated. The preheating and water-cooling-assisted deposition simultaneously increases the tensile strength and elongation of the deposited samples. The combination of preheating and instant cooling improves the deposition efficiency of FRAM and weakens the thermal-softening effect.

Key words: Friction rolling additive manufacturing, Al-Li alloy, Plasma preheating, Instant cooling, Heat accumulation, Microstructure