Second phase particles and mechanical properties of 2219 aluminum alloys processed by an improved ring manufacturing process

Abstract

2219 Al alloy has been used to manufacture the launch vehicle storage tank transition ring, but the large ring obtained in conventional manufacturing processes still suffers from severely agglomerated coarse second phase particles and poor mechanical properties. An improved process (forging at 510 °C with 20% deformation and at 240 °C with 50% deformation, then rolling at 240 °C with 30% deformation, followed by solid solution at 538 °C for 4 h and T8 treatment) for 2219 Al alloy large ring manufacturing was proposed, and the corresponding simulation tests were carried out. The evolution of Al₂Cu second phase particles and the mechanical properties of the produced workpieces were investigated. The results showed that the degree of crushing, dissolution, and precipitation of Al₂Cu particles were significantly improved in the improved process, and the area fractions of Al₂Cu coarse second phase particles after saddle forging and rolling were significantly reduced, leading to 2.4 times increase in area fraction of the θ′ phase after T8 treatment. More homogeneous slip occurred during the tensile testing process and intergranular fracture was the main fracture mechanism. The tensile strength σ_b, yield strength σ_s, and elongation δ in the radial direction of the 2219 workpieces were increased to 491 MPa, 388 MPa, and 13.1%, where were increases of 11%, 14%, and 68%, respectively. The uniformity in σ_b, σ_s, and δ of the 2219 workpieces increased by 57%, 38%, and 64%, respectively.

Introduction

Owing to its excellent weldability and high and low temperature mechanical properties, 2219 Al alloy has been widely applied to large ring manufacturing in aviation, aerospace, navigation, and military applications [[1], [2], [3], [4], [5]]. At present, ring rolling technology (RRT) is the most popular way to manufacture large ring [[6], [7], [8], [9]], which has attracted a large number of scholars [[10], [11], [12], [13], [14], [15], [16]]. However, current research on 2219 aluminum alloy is primarily focused on basic research [[17], [18], [19], [20], [21]], where the only relevant research on the RRT of 2219 Al alloy large ring shows that there are many defects in the manufacturing process, such as agglomerated Al₂Cu coarse second phase particles (CSPP), low mechanical properties, and poor uniformity [[22], [23], [24]]. Therefore, 2219 Al alloy large ring manufacturing technology is still in urgent need of further development, and its mechanical properties and uniformity should be further enhanced.

Generally, RRT includes severe plastic deformation (SPD), saddle forging, and rolling. Existing research focuses on SPD and rolling, while there are no reports on saddle forging technology and the co-processing of saddle forging and rolling. For example, Zha and Ma et al. [25,26] studied the effects of equal-channel angular pressing on microstructural evolution and mechanical properties of Al-7Mg alloy. Sitdikov et al. [27] analyzed the influence of temperature on microstructural and mechanical properties of Al-Mg alloy in multidirectional forging. Nageswara et al. [28] investigated the effects of deformation on microstructure and mechanical properties of 6061 Al alloy in multidirectional forging at low temperature. Based on high temperature RRT, Tang and Hu et al. [29,30] revealed the influences of rolling parameters on microstructure evolution of IN718 and GH4738 Nickel.

Preliminary studies indicated that during the radial-axial ring rolling process, alloy materials typically flow in the circumferential direction and form a large amount of fibrous tissue, resulting in higher mechanical properties in the circumferential direction compared to those in the radial and axial directions. Furthermore, the mechanical property differences between the circumferential and the other two directions increased with increasing rolling deformation. Hence, it is expected to improve the uniformity in mechanical properties by adjusting and controlling the saddle forging and rolling deformations.

In addition, relevant literature shows that lowering the deformation temperature is helpful to break and refine the coarse second phase particles [31,32]. The microstructure of 2219 Al alloy ring may be further improved by using warm deformation in the saddle forging process, which is likely to improve the mechanical properties of the ring.

Therefore, an improved process (forging at 510 °C with 20% deformation and at 240 °C with 50% deformation, then rolling at 240 °C with 30% deformation, followed by solid solution at 538 °C for 4 h and T8 treatment) for 2219 Al alloy ring is proposed in the present study. The evolution of Al₂Cu second phase particles and the mechanism for improving the mechanical properties of 2219 Al alloy rings were systematically analyzed, so as to provide a basis and reference in developing the high-performance manufacturing process of the 2219 Al alloy storage tank transition ring.