Tensile and Fatigue Strength, Fatigue Crack Propagation Rate, and Fracture Behavior of CaO-Added AM30 Alloy

IF 3.3 3区材料科学 Q2 MATERIALS SCIENCE, MULTIDISCIPLINARY Metals and Materials International Pub Date : 2024-05-18 DOI:10.1007/s12540-024-01695-9

Min-Seok Baek, Abdul Wahid Shah, Shae K. Kim, Hyun-Kyu Lim, Kee-Ahn Lee

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Abstract

This work investigated the tensile and fatigue strength, fatigue crack propagation rate and corresponding mechanism, and fracture behavior (under the tensile and cyclic loading) of the extruded CaO-AM30 alloy. The microstructure observations shown that the average grain size of AM30 base alloy was 7.8 μm, which decreased to 3.5 μm in the CaO-AM30 alloy. In both alloys, Mg₁₇Al₁₂ and Al6(Mn, Fe) phases were present, and C15 ((Mg, Al)₂Ca) phases were additionally present in the CaO-AM30 alloy. Also, the average size of the Mg₁₇Al₁₂ and Al6(Mn, Fe) phases was much smaller in the CaO-AM30 alloy than those in the AM30 alloy. As a result of the smaller grains and fine evenly distributed second phases, CaO-AM30 alloy shown an improved tensile strength along with a 25% increase in the elongation. Accordingly, the CaO-AM30 alloy showed higher fatigue strength (168 MPa) than the AM30 alloy (130 MPa) after ~ 10⁷ number of cycles. Nevertheless, fatigue crack growth test revealed that the CaO-AM30 alloy has a lower threshold ∆K_th value than the AM30 base alloy. Also, the calculated value for m (log slope of da/dN and ∆K) was 13.64 for AM30 alloy, which increased to 14.15 for the CaO-AM30 alloy. The relatively higher crack propagation rate of the CaO-AM30 was most likely related to the presence of larger plastic deformation zone in it than its grain size, causing the suppression of fatigue crack closure mechanism during the unloading half of the cycle. Hence, this study suggested that the fine grains improve the strength and high-cycle fatigue properties of the Mg alloys, but adversely affect the fatigue crack propagation resistance.

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添加氧化钙的 AM30 合金的拉伸和疲劳强度、疲劳裂纹扩展率以及断裂行为

这项工作研究了挤压 CaO-AM30 合金的拉伸和疲劳强度、疲劳裂纹扩展速率和相应机制以及断裂行为（在拉伸和循环加载下）。微观结构观察结果表明，AM30 基本合金的平均晶粒尺寸为 7.8 μm，而 CaO-AM30 合金的平均晶粒尺寸则减小到 3.5 μm。两种合金中都存在 Mg17Al12 和 Al6（锰、铁）相，CaO-AM30 合金中还存在 C15（（镁、铝）2Ca）相。此外，CaO-AM30 合金中 Mg17Al12 和 Al6（锰，铁）相的平均尺寸也比 AM30 合金中的小得多。由于晶粒更小，第二相分布更均匀，CaO-AM30 合金的抗拉强度得到提高，伸长率增加了 25%。因此，在经过约 107 次循环后，CaO-AM30 合金的疲劳强度（168 兆帕）高于 AM30 合金（130 兆帕）。然而，疲劳裂纹生长测试表明，CaO-AM30 合金的阈值 ∆Kth 值低于 AM30 基本合金。此外，AM30 合金的 m（da/dN 和 ∆K 的对数斜率）计算值为 13.64，而 CaO-AM30 合金的 m 计算值则增至 14.15。CaO-AM30 的裂纹扩展速率相对较高，这很可能与它存在比其晶粒大度更大的塑性变形区有关，导致疲劳裂纹闭合机制在卸载半周期受到抑制。因此，这项研究表明，细晶粒可提高镁合金的强度和高循环疲劳性能，但会对抗疲劳裂纹扩展能力产生不利影响。

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来源期刊

Metals and Materials International 工程技术-材料科学：综合

CiteScore

7.10

自引率

8.60%

发文量

197

审稿时长

3.7 months

期刊介绍： Metals and Materials International publishes original papers and occasional critical reviews on all aspects of research and technology in materials engineering: physical metallurgy, materials science, and processing of metals and other materials. Emphasis is placed on those aspects of the science of materials that are concerned with the relationships among the processing, structure and properties (mechanical, chemical, electrical, electrochemical, magnetic and optical) of materials. Aspects of processing include the melting, casting, and fabrication with the thermodynamics, kinetics and modeling.