Method to decode stress-strain diagrams to identify the structure-strength relationships in aged aluminum alloys

Significance 

The failure of structures resulting from failure of the basic material components is often dictated by the material performance in response to local stresses and strains. This performance is itself determined by the structural makeup of the component materials at all length scales. For example, crystalline line defects present in metals and their alloys determine their desirable ductility properties while localized accumulation of vacancies to form cracks can lead to catastrophic ductile failure.

The question is, however, how to obtain the desired material property that best suit a particular application such as in vehicle design and construction. Recently, a significant research effort has led to several innovations that have addressed the challenges inherent in adapting industry-standard processing methods to optimize the properties of materials for specific applications. For example, alloys are formed by combining two or more metals (which combine to form intermetallic compounds) of different properties to result in a final product of relatively unique properties. This is the physical metallurgy route currently taken by most metal forming industries.

The current and widely practiced methods for determining whether or not different materials meet the required technical specifications involve standard tensile tests and measurement of the ultimate tensile strength. However, there is a real need to take into consideration the complex spectrum of defect structures, at the microscopic scale, that are introduced by the metal forming process as these are known to play a major role in determining the strength and ductility of the final product.

Research conducted by Shigeo Saimoto, Marsha A. Singh, and Michael R. Langille at Queen’s University in collaboration with Julie Levesque from Laval University, Kaan Inal from University of Waterloo, Marek Niewczas from McMaster University and Arthur R. Woll at Cornell University in the United States developed a new method of analyzing the strength and structure behaviors and crystalline deformation and failure mechanisms exhibited by aluminum alloys. The technique involves inputting the available standard stress-strain data into the constitutive relation analyses (CRA) method. The research work has been published in the journal, Materials Science and Engineering A.

In their studies, the research team carried out industrial extrusion on AA6063 aluminum alloys to demonstrate how to achieve the required materials properties by applying various changes to the thermo-mechanical processing involved in the extrusion process. They also used high intensity x-ray scattering methods, supplemented by electron microscopy, to detect the microstructure defects and formation that cause ductile failure in such materials.

The researchers observed that the CRA method could be effectively applied to optimization of the desired material properties as it aids quality control while also facilitating industrial process trouble-shooting processes aimed at checking the functionality of the various conditions.

According to the authors, the CRA method is a versatile tool. For instance, it can be used to supplement the characterization of the atomic microstructure obtained in previous studies, as illustrated by CRA of pipe-line steel previously reported in Advances in Engineering. As a result, this method can be used to determine the changes occurring in the alloys which can help in effective design of the process. The results of the study will improve the industrial metal processing practice leading to improved alloys selection and the realization of various designed properties for the materials.

Acknowledgement:

The authors thank the Natural Sciences and Engineering Research Council of Canada for support of continuing studies on plasticity of age-hardenable alloys. The studies at Queen’s and McMaster Universities were coordinated by the NSERC program of Automotive Partnership Council commissioned at Waterloo University under Professor K. Inal. We are grateful to Cornell High Energy Synchrotron Service (CHESS) for providing beam-time under supervision of Dr. A. Woll to carry out this work.

 

Reference

Saimoto, S., Singh, M.A., Langille, M.R., Levesque, J., Inal, K., Niewczas, M., & Woll, A.R. (2018). Method to decode stress-strain diagrams to identify the structure-strength relationships in aged aluminum alloys. . Materials Science and Engineering: A, 709, (2018) 9-16.

 

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