Effect of Mn addition on microstructure and mechanical properties of cast Al-2Li-2Cu-0.8Mg-0.4Zn-0.2Zr alloy
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of 0.5 wt% Mn addition on the microstructure and mechanical properties of cast Al–2Li–2Cu–0.8Mg–0.4Zn–0.2Zr (wt%) alloy was investigated. Results showed that the grain size of Mn-containing alloy was smaller than that of Mn-free alloy in both the as-cast and solution treated state. Al20Mn3Cu2 dispersoids were formed during solution treatment in the Mn-containing alloy. After aging at 175 °C for 32 h, a large volume fraction of coherent Al3Li/Al3(Li, Zr) particles were precipitated in both Mn-free and Mn-containing alloys, while more Guinier–Preston– Bagaratsky zones were observed in the Mn-free alloy. Mn addition improved the elongation significantly, which was 1.7% for Mn-free alloy and 3.3% for the alloy with 0.5 wt% Mn addition.
I. INTRODUCTION
Al–Li alloys have been widely concerned recently for their lower densities, higher strengths, and stiffness to weight ratio compared to other conventional Al alloys.1–3 As reported, each 1 wt% increment of Li addition (up to 4 wt %, all compositions are in wt% hereafter unless otherwise noted) into Al alloys can reduce density by 3% and simultaneously increase elastic modulus by about 6%.4 Therefore, Al–Li alloys, such as AA2099, AA2195 etc., have received extensive attentions in aerospace, military, and commercial applications which strongly require weight critical and stiffness-critical structures. However, the existing aerospace applications of Al–Li alloys are mostly wrought alloys. There is still lack of data on cast Al–Li alloys. This situation is mainly because that the wrought Al–Li alloys have the superior mechanical properties to cast alloys. Casting is not only a low-cost way to manufacture products with complex shapes, but also an effective method to mitigate the anisotropy of mechanical properties. Moreover, the weight reduction could be much more effective in cast condition, since the limitation of Li addition can be much higher than that in wrought alloys. Therefore, it is important to investigate the cast Al–Li alloys. Drits et al.5 reported that casting Al alloys containing 2 wt% Cu and 1–2 wt% Li have reasonable high mechanical properties [ultimate tensile strength (UTS) 5 350 MPa, elongation (EL) 5 2–3%] in the full aged condition. Moreover, some other alloying elements (such as Mg, Zn, etc.) are usually added into Al–Li alloys Contributing Editor: Jürgen Eckert Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2015.408 250
J. Mater. Res., Vol. 31, No. 2, Jan 28, 2016
to further improve the strength. It was reported that Mg addition lowered the solubility of Li in Al matrix, thereby increasing the tensile strength of Al–Li alloys by enhanced precipitation of fine Al3Li phases.6 Hirosawa et al.7 also found that a small amount of Mg addition (0.5%) to Al–1.35Li–5.5Cu–0.4Ag–0.15Zr alloy resulted in an enhanced age-hardening response. Recent research by Gable8 indicated that Zn addition to an Al–1Li–4Cu alloy facilitated the T1 (Al2CuLi) matrix nucleation, which is the primary stre
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