Microstructure-strength correlations in Al-Si-Cu alloys micro-alloyed with Zr

Mondol, S and Bansal, U and Singh, MP and Dixit, S and Mandal, A and Paul, A and Chattopadhyay, K (2022) Microstructure-strength correlations in Al-Si-Cu alloys micro-alloyed with Zr. In: Materialia, 23 .

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Abstract

The paper presents the microstructure-strength correlation of copper mould cast thin section of Al-(6–8)Si-Cu (at%). The efficacy of small Zr addition (0.15at%) and three-stage heat treatment on these alloys for achieving superior high-temperature mechanical properties were evaluated. The addition of Zr refines the alloy microstructure, exhibits a feather-like eutectic morphology in the interdendritic spaces and Zr supersaturation in the dendrites. Direct ageing at 450 ℃ yields coherent, spherical, L12 order Al3Zr precipitates of size 9–11 nm in the α-Al matrix. A characteristic composite microstructure of fine θʹ plates (∼58–67 nm in length and ∼4 nm in thickness) on these Al3Zr precipitates could be developed on ageing at 190 ℃ following a brief solution treatment at 500 ℃. The plates are finer in size when compared to that formed in alloys without Zr for similar heat treatment (Al-6Si-Cu:∼234 nm in length and ∼9.3 nm in thickness). Composition analysis has established Zr and Si partitioning in θ′ plates that impart long-term thermal stability and coarsening resistance at 250 °C. The observed complexity of the microstructure with a finer length scale rationalizes the high yield strength of the Zr modified alloys (306–320 MPa at room temperature), which is 1.7 times higher than the corresponding Al-6Si-Cu alloy. At 250 °C, the observed tensile yield strength is ∼140 MPa. A detailed analysis with available models using quantitative microstructural parameters enable rationalization of our observations

Item Type:	Journal Article
Publication:	Materialia
Publisher:	Elsevier B.V.
Additional Information:	The copyright for this article belongs to the Elsevier B.V.
Keywords:	Age hardening; Binary alloys; Coarsening; Copper alloys; High resolution transmission electron microscopy; High strength alloys; Morphology; Ostwald ripening; Silicon alloys; Yield stress; Zircaloy, Alloy microstructure; Copper moulds; Direct aging; Eutectic morphology; High temperature strength; High-temperature mechanical properties; Interdendritic space; matrix; Thin-sections; Zr addition, Aluminum alloys
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	05 Jun 2022 06:15
Last Modified:	05 Jun 2022 06:15
URI:	https://eprints.iisc.ac.in/id/eprint/73107

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