电弧增材制造 AZ91/Ti6Al4V 异种合金微观组织和性能

Microstructure and Properties of AZ91/Ti6Al4V Dissimilar Alloys Fabricated by Wire Arc Additive Manufacturing

摘要

镁合金及钛合金作为典型的轻质合金材料，被广泛应用于轨道交通、航空航天和生物工程等领域，通过制备镁/钛异种合金构件来实现镁合金和钛合金的优势互补，不仅能够满足更多现代工程需求，还可以进一步拓展二者的应用深度与广度．针对镁/钛异种合金构件实际生产制造需求，采用电弧增材制造(WAAM)技术制备了AZ91 镁合金/Ti6Al4V 钛合金异种合金试件，探究了镁合金熔敷参数对试件宏观成形及界面组织的影响，在此基础上分析了镁/钛异种合金WAAM 试件的微观组织、力学性能和腐蚀性能，并结合Mg-Ti-Al 三元系统热力学计算探讨了镁/钛异种合金WAAM 试件的界面反应层形成机理．结果表明：镁合金熔敷时过大的送丝速度会导致镁合金的蒸发损耗增加，而较低的行进速度则会导致镁合金熔敷层侧向流淌严重；在镁/钛界面层形成了Ti3Al 和Mg17Al12 金属间化合物，且界面层的厚度随着镁合金熔敷时热输入的增加而增加．在拉伸测试过程中，镁/钛异种合金水平(横向)拉伸试件不仅在Ti-Al 与Mg-Al 金属间化合物层之间发生剪切失效，使得拉伸试件的钛合金熔敷层与镁合金熔敷层产生分离，还发生了钛合金熔敷层断裂与镁合金熔敷层断裂，在试件横截面积为6 mm² 且两种合金熔敷层面积比为1∶1条件下，其平均最大拉伸剪切载荷为(3 203±155)N．与钛合金熔敷层相比，镁合金熔敷层具有较高的自腐蚀电流密度和较低的自腐蚀电位，使得镁/钛异种合金试件易发生电偶腐蚀；在质量分数为3.5%的NaCl 溶液浸泡腐蚀过程中，镁合金熔敷层作为阳极发生溶解形成点蚀坑，钛合金熔敷层则作为阴极发生析氢反应，最终在界面处形成大量的Mg(OH)₂．热力学计算结果显示：在熔敷沉积过程中，Al 原子受到化学势的驱动而向界面处扩散，并在界面处先后形成Ti-Al 和Mg-Al 金属间化合物.

Abstract

Magnesium(Mg) and titanium(Ti) alloys，as typical lightweight metallic materials，are widely used in rail transportation，aerospace，and biomedical engineering. The fabrication of Mg/Ti dissimilar alloy components， which combine the advantages of both materials，not only meets the growing demands of modern engineering applications but also extends their potential applications in depth and breadth. To meet the practical manufacturing requirements of Mg/Ti dissimilar alloy components，wire arc additive manufacturing(WAAM) was employed to fabricate AZ91 Mg alloy and Ti6Al4V Ti alloy dissimilar alloy specimens. This study investigated the influence of Mg alloy deposition parameters on the macromorphology and interfacial microstructure of the specimens. Based on these investigations，the microstructure，mechanical properties，and corrosion performance of the WAAM-fabricated Mg/Ti dissimilar alloy specimens were comprehensively analyzed. Furthermore，the formation mechanism of the interfacial reaction layer was clarified through thermodynamic calculations of the Mg-Ti-Al ternary system. The results demon- strated that excessively high wire feed speed during Mg alloy deposition led to increased evaporation loss，whereas insufficient travel speed caused severe lateral flow of the Mg alloy cladding layer. Ti3Al and Mg17Al12 intermetallic compounds(IMCs) formed at the Mg/Ti interface layer，and the interface thickness increased with increasing heat input during Mg alloy deposition. During tensile testing，the horizontal (transverse) tensile samples of the Mg/Ti dissimilar alloy specimens experienced shear failure at the interface between the Ti-Al and Mg-Al IMC layers， leading to separation of the Ti and Mg alloy cladding layers. The Ti alloy and Mg alloy cladding layers also fractured.At a sample cross-sectional area of 6 mm² while two deposited alloy layers occupied equal proportions of this cross-sectional area，the average maximum tensile shear load was (3 203±155) N. Compared with the Ti alloy cladding layer，the Mg alloy cladding layer exhibited a higher self-corrosion current density and a lower self-corrosion poten- tial，making Mg/Ti dissimilar alloy specimens more susceptible to galvanic corrosion. During immersion corrosion testing in 3.5%(mass fraction) NaCl solution，the Mg cladding layer acted as the anode and underwent preferential dissolution，forming characteristic pitting corrosion morphologies，while the Ti cladding layer acted as the cathode， where visible hydrogen evolution occurred. This electrochemical process ultimately resulted in Mg(OH)2 formation at the interfacial region. Thermodynamic calculations revealed that during deposition，Al atoms underwent chemical- potential-driven diffusion toward the interface，where they sequentially formed Ti-Al and Mg-Al IMCs.

关键词

镁/钛异种合金 / 电弧增材制造 / 微观组织 / 力学性能 / 腐蚀性能 / 热力学计算

Key words

magnesium/titanium dissimilar alloy / wire arc additive manufacturing / microstructure / mechanical property / corrosion performance / thermodynamic calculation

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基金资助

国家自然科学基金资助项目(52075377)