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.
Highlights
Published: 26 February 2021Aluminum alloys of the 6xxx series are of major technological importance and have been studied extensively
With the addition of Cu, the quaternary lath-shaped phase Q’ further contributes to the strengthening [4,5]. These metastable phases are precursors for the stable phases of β (Mg2 Si) and Q (Al5 Cu2 Mg8 Si6 ), respectively [4], and the precipitation sequence is generally accepted as follows [4,5,6,7,8]: At room temperature, Mg-Si co-clusters evolve from a super-saturated solution
The significant difference between these two conditions was the absence of peak I for the pre-aged condition
Summary
Aluminum alloys of the 6xxx series are of major technological importance and have been studied extensively. Because of their good formability combined with their precipitation hardening ability, they are attractive to the automotive and aircraft industries. With the addition of Cu, the quaternary lath-shaped phase Q’ further contributes to the strengthening [4,5] These metastable phases are precursors for the stable phases of β (Mg2 Si) and Q (Al5 Cu2 Mg8 Si6 ), respectively [4], and the precipitation sequence is generally accepted as follows [4,5,6,7,8]: At room temperature, Mg-Si co-clusters evolve from a super-saturated solution. Nanoscale precipitates with an ordered arrangement of Mg-, Si- and
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