Towards Friction Stir Remanufacturing of High‑Strength Aluminum Components

Volumetric defects in high-strength aluminum alloy components were repaired via friction stir remanufacturing(FSR).Various consumable pins made of AA7075-T6 were designed.Top diameters of the consumable pins afected material fow,which ensured that the materials at the repairing interface were forged to metallurgical bonding.Conical angles determined load transfer besides material fow,which afected the fracture of the pins before the dwelling stage.Sound repaired components were achieved when the conical angle of the consumable pin was 1°larger than that of the volumetric defect.The ultimate tensile strength and elongation of the repaired components reached 445.9 MPa and 9.6%,respectively.The design criteria of the consumable pin in the FSR was established,which provided valuable references to repair volumetric defects in high-strength aluminum components.

Effect of Multiple Thermal Cycles on Microstructure and Mechanical Properties of Cu Modified Ti64 Thin Wall Fabricated by Wire-Arc Directed Energy Deposition

This study investigated the effect of thermal cycles on Cu-modified Ti64 thin-walled components deposited using the wire-arc directed energy deposition(wire-arc DED)process.For the samples before and after experiencing thermal cycles,it was found that both microstructures consisted of priorβ,grain boundaryα(GBα),and basketweave structures containingα+βlamellae.Thermal cycles realized the refinement ofαlaths,the coarsening of priorβgrains andβlaths,while the size and morphology of continuously distributed GBαremained unchanged.The residualβcontent was increased after thermal cycles.Compared with the heat-treated sample with nanoscale Ti2Cu formed,short residence time in high temperature caused by the rapid cooling rate of thermal cycles restricted Ti2Cu formation.No formation of brittle Ti2Cu means that only grain refinement strengthening and solid-solution strengthening matter.The yield strength increased from 809.9 to 910.85 MPa(12.46%increase).Among them,the main contribution from solid solution strengthening(~51 MPa)was due to the elemental redistribution effect betweenαandβphases caused by thermal cycles through quantitative analysis.The ultimate tensile strength increased from 918.5 to 974.22 MPa(6.1%increase),while fracture elongation increased from 6.78 to 10.66%(57.23%increase).Grain refinement ofαlaths,the promotedα′martensite decomposition,decreased aspect ratio,decreased Schmid factor,and local misorientation change ofαlaths are the main factors in improved ductility.Additionally,although the fracture modes of the samples in the top and middle regions are both brittle-ductile mixed fracture mode,the thermal cycles still contributed to an improvement in tensile ductility.