Influence of Pre-Aging on the Artificial Aging Behavior of a 6056 Aluminum Alloy after Conventional Extrusion

Abstract

In the present study, the influence of the initial heat-treatment conditions on the artificial aging behavior after conventional linear extrusion at room temperature was investigated for the precipitation hardening of a 6056 aluminum alloy. A solution-annealed condition was systematically compared to naturally-aged and pre-aged conditions. Differential scanning calorimetry was used for analyzing the precipitation sequence and its dependence on the initial heat treatment. The natural aging behavior prior to extrusion and the artificial aging behavior after extrusion were determined by microhardness measurements as a function of the aging time. Furthermore, the microstructure, dependent on the induced strain, was investigated using optical microscopy and transmission electron microscopy. As a result of pre-aging, following a solid-solution treatment, the formation of stable room-temperature clusters was suppressed and natural aging was inhibited. The artificial aging response after extrusion was significantly enhanced by pre-aging, and the achieved hardness and strength were significantly higher when compared with the equally processed solution-annealed or naturally-aged conditions.

Research on Alloy Design and Process Optimization of Al–Mg–Zn-Cu-Based Aluminum Alloy Sheets for Automobiles with Secured Formability and Bake-Hardenability

“…H. Jiang et al [33] reported that high-density dispersed precipitation of the η'-phase, the main reinforcing phase of AA7055 alloy, was improved through pre-aging and, X. Liao et al [34] reported that the main reinforcing phase, the η'-phase, was formed more finely with a higher volume fraction through the application of pre-aging to Al-Zn-Mg-Cu alloys. Also, L. Winter et al [35] reported that by applying pre-aging to AA6056 alloy, the formation of room-temperature clusters and natural aging were suppressed after solid solution treatment, and the artificial aging reactivity was greatly improved. It was confirmed that pre-aging was advantageous to the mechanical properties of the designed alloy based on the size of the precipitate phases that were maintained at a smaller size through pre-aging and the number density of the precipitate phases per unit area.…”

Combined Effect of Particle Reinforcement and T6 Heat Treatment on the Compressive Deformation Behavior of an A357 Aluminum Alloy at Room Temperature and at 350 °C

“…During the subsequent heating (e.g., prior to hot compression testing), these (caused by the low cooling rate) sparsely distributed precipitates grow while their coherency decreases. However, it can be assumed that the precipitation kinetic during testing at 350 • C of the as-sintered conditions starts with the formation of GP I zones at about 190 • C, see Figure 5 (I), which indicates that Si-, Mg-and Mg-Si co-clusters were already present after sintering [9]. This peak is followed by the overlapping formation of β ′′ (III), β' (IV) and β (V) precipitates, from about 240 • C to 380 • C. At about 380 • C, the precipitation ends and the dissolution of the Mg 2 Si phases begins for both conditions.…”

“…In addition, the presence of the alloying elements Si and Mg allows for a significant improvement in strength due to precipitation hardening. The precipitation sequence is generally accepted as [7][8][9]: super saturated solid solution → clusters → Guinier-Preston zones (GP I, coherent) → β ′′ (semi-coherent, needle-shaped) → β ′ (semi-coherent, rod-shaped) → β (incoherent). The highest strength can be achieved by a T6 heat treatment routine, i.e., solution annealing, water quenching and artificial ageing at elevated temperatures to achieve a high amount of finely dispersed β ′′ precipitates.…”

Influence of Artificial Aging Time on Microstructures and Mechanical Properties of Porthole Die Extruded 6063 Aluminum Alloy

“…Yang et al [14] found that aging time had a significant impact on the anti-corrosion resistance of the 6061-T6 aluminum alloy due to the content of the β phase. Winter et al [15] reported that pre-aging enhanced the effect of artificial aging on the hardness and strength of the 6056 aluminum alloy.…”