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<p>This study proposes a novel solid-contact active cooling (SCAC) method to address the trade-off between manufacturing rate and material quality in wire-arc directed energy deposition (DED) of AZ31 magnesium alloys. Three conditions were evaluated: no active cooling (NAC), SCAC using copper blocks (SCAC-C), and SCAC with internal water circulation (SCAC-W). Experimental results demonstrated that even when the copper blocks in SCAC-C reached 500&#xa0;°C under a short inter-layer dwell time of 18&#xa0;s, it facilitated higher cooling rates and finer grain structures than NAC. Most significantly, SCAC-W consistently outperformed both NAC and SCAC-C, achieving superior tensile strength and ductility at the same 18&#xa0;s interval. While NAC under these high-efficiency conditions resulted in a coarse average grain size of 148&#xa0;μm, SCAC-W maintained a refined microstructure of 43&#xa0;μm. Quantitative comparison between the calculated Hall-Petch contribution and experimental data suggested that this grain refinement was the dominant factor enhancing the 0.2% yield strength. Furthermore, fractographic observations revealed that SCAC-W exhibited a mixed-mode fracture surface with deep dimples, indicating enhanced intragranular ductile fracture, whereas NAC was dominated by transgranular cleavage. The rapid cooling in SCAC-W also promoted the formation of η-Al<sub>8</sub>Mn<sub>5</sub> precipitates while suppressing coarse β-Mg<sub>17</sub>Al<sub>12</sub> phases. This study concludes that SCAC-W is the most effective strategy for high-productivity Mg alloy additive manufacturing, ensuring excellent mechanical performance even at minimized inter-layer dwell times.</p>

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Effect of the active cooling and dwell time to tensile properties of AZ31 wall components by wire-arc directed energy deposition

  • 期刊论文

  • 发表日期：

    2026年4月1日

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  • Hideaki Nagamatsu,
  • Hiroyuki Sasahara

摘要

This study proposes a novel solid-contact active cooling (SCAC) method to address the trade-off between manufacturing rate and material quality in wire-arc directed energy deposition (DED) of AZ31 magnesium alloys. Three conditions were evaluated: no active cooling (NAC), SCAC using copper blocks (SCAC-C), and SCAC with internal water circulation (SCAC-W). Experimental results demonstrated that even when the copper blocks in SCAC-C reached 500 °C under a short inter-layer dwell time of 18 s, it facilitated higher cooling rates and finer grain structures than NAC. Most significantly, SCAC-W consistently outperformed both NAC and SCAC-C, achieving superior tensile strength and ductility at the same 18 s interval. While NAC under these high-efficiency conditions resulted in a coarse average grain size of 148 μm, SCAC-W maintained a refined microstructure of 43 μm. Quantitative comparison between the calculated Hall-Petch contribution and experimental data suggested that this grain refinement was the dominant factor enhancing the 0.2% yield strength. Furthermore, fractographic observations revealed that SCAC-W exhibited a mixed-mode fracture surface with deep dimples, indicating enhanced intragranular ductile fracture, whereas NAC was dominated by transgranular cleavage. The rapid cooling in SCAC-W also promoted the formation of η-Al8Mn5 precipitates while suppressing coarse β-Mg17Al12 phases. This study concludes that SCAC-W is the most effective strategy for high-productivity Mg alloy additive manufacturing, ensuring excellent mechanical performance even at minimized inter-layer dwell times.