熱處理過程中Mg-8Gd-3Y-1Nd-0.5Zr合金的組織演變及性能

熱處理過程中Mg-8Gd-3Y-1Nd-0.5Zr合金的組織演變及性能Microstructure evolution and performance of Mg-8Gd-3Y-1Nd-0.5Zr alloy during heat treatment

采用透射電鏡、掃描電鏡、能譜分析、X射線衍射及力學(xué)性能等測(cè)試手段，研究熱處理工藝對(duì)水冷鑄造的Mg-8Gd-3Y-1Nd-0.5Zr(質(zhì)量分?jǐn)?shù))合金顯微組織、力學(xué)性能和耐腐蝕性能的影響。合金鑄態(tài)顯微組織由α-Mg、Mg(Gd,Y)相、富Zr小顆粒相和β-Mg24Y5網(wǎng)狀共晶組成。在520 ℃固溶24 h后，合金中共晶相固溶進(jìn)基體，固溶演變過程為α-Mg+β-Mg24Y5相+ Mg(Gd,Y)→過飽和α-Mg固溶體+Mg(Gd,Y)相。225 ℃時(shí)效，合金的析出序列為 Mg(S.S.S.S)→β″(DO19)→β′(CBCO)→β1(FCC)→β(FCC)，時(shí)效24 h達(dá)到峰時(shí)效態(tài)，合金的室溫抗拉強(qiáng)度達(dá)到 231 MPa，伸長(zhǎng)率為 3.4%。時(shí)效處理能提高合金耐腐蝕性能，225 ℃時(shí)效72 h時(shí)合金析出穩(wěn)定β(FCC)相，平均析氫速率最小，為0.22 mL/(cm2·h)，合金的耐腐蝕性能最強(qiáng)。

The effects of heat treatments on the microstructures and properties of the Mg-8Gd-3Y-1Nd-0.5Zr alloy were studied. The cast Mg-8Gd-3Y-1Nd-0.5Zr alloy consists α-Mg, Mg(Gd,Y) second phases and eutectic phases of Zr-rich particle phase and β-Mg24Y5 reticular. After solid solution treatment at 520 ℃ for 24 h, the microstructure evolution of the alloy follows this sequence, α-Mg+β-Mg24Y5 phase + Mg(Gd,Y)→oversaturated α-Mg solid solution +Mg(Gd,Y) phase. After aged at 225 ℃, the second phases in the Mg-8Gd-3Y-1Nd-0.5Zr alloy precipitate following this sequence, Mg(S.S.S.S)→β″(DO19)→β′(CBCO)→β1(FCC)→β(FCC). The peak aging state occurs when the alloy is aged at 225 ℃ for 24 h. The room temperature tensile strength gets 231 MPa and the elongation rate gets 3.4%, respectively. Moreover, aging treatment improves the corrosion resistance of the alloy. After aged at 225 ℃ for 72 h, stable β(FCC) phase precipitates in the Mg-8Gd-3Y-1Nd-0.5Zr alloy, which express the best corrosion resistance. The lowest average hydrogen precipitation rate is 0.22 mL/(cm2·h).

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