Evolution of the Second-Phase Particles and Their Effect on Tensile Fracture Behavior of 2219 Al-xCu Alloys

Daofen Xu,Yunqiang Chen,Songyi Chen,Kanghua Chen

doi:10.3390/met10020197

Abstract

In this study, the continuous evolution of the second-phase particles across as-cast, homogenization, multi-directional forging (MDF), and solution-aging treatment and their effect on tensile fracture behavior of 2219 aluminum alloys with different Cu contents was examined by optical microscopy (OM), scanning electron microscopy (SEM), and tensile tests. The results showed that the microstructure of as-cast 2219 aluminum alloy consisted of the α-Al matrix, Al2Cu coarse phase, and Fe-rich impurity phase. Severe segregation of Cu existed, and eutectic networks can be observed in the ingot. With an increase in Cu content, the eutectic networks became coarsen and thicker. During the complex improved process, the refinement mechanisms were fragmentation, dissolution, and diffusion of Al2Cu particles. Most fine Al2Cu particles were fully dissolved into the matrix and partial coarse particles were still retained after solution-aging treatment. Thus, the elongations of all the samples, undergoing solution treatment followed by water quenching, increased evidently. Then, the elongations decreased slightly due to the increase of precipitates. The fractography analysis of peak aged condition samples indicated that the fracture mode was diverted from a typical inter-granular fracture to a mainly trans-granular fracture with increase in Cu content from 5.56% to 6.52%. Fracture initiation mainly occurred by original microcrack propagation and microvoid nucleation at the coarse constituents.

Highlights

Because of its high specific strength, excellent corrosion resistance, good machinability, and sound weldability, the 2219 aluminum alloy has been extensively used to fabricate propellant tank of large launch vehicles, such as Saturn 5 and Long March 5 series launch vehicle [1,2]
They exhibited typical dendrite structure in the ingotsinand the dendrite increased with contents.a They exhibited a typical dendrite structure the ingots and the segregation dendrite segregation increase in Cu contents
The evolution of the second-phase particles during as-cast, homogenization, multi-directional forging (MDF), and solution treatment was conducted on the 2219 Al-xCu alloys

Summary

Introduction

Because of its high specific strength, excellent corrosion resistance, good machinability, and sound weldability, the 2219 aluminum alloy has been extensively used to fabricate propellant tank of large launch vehicles, such as Saturn 5 and Long March 5 series launch vehicle [1,2]. The low melting point of Al2 Cu eutectic phase can reduce the tendency of hot cracking during the welding, it brings some adverse effects. Cu across the ultra-large 2219 Al alloy ingot and found that the coarse Al2 Cu particles could not be completely dissolved even after a complex thermo-mechanical treatment (TMT) process, and the un-dissolved particles were subjected to stress concentration during deformation and acted as Metals 2020, 10, 197; doi:10.3390/met10020197 www.mdpi.com/journal/metals. Huang et al [5] investigated the effect of the shape and size of particles on void nucleation mechanism and found that coarse particles with a high shape factor were concluded to be preferable for inducing the formation of cracks and accelerating the coalescence of micro-cracks. Yu et al [6] reported that coarse Al2 Cu particles can be elongated during the ring rolling process, which could be the main reason for anisotropy of mechanical properties

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