Joint effect of micro-sized Si particles and nano-sized dispersoids on the flow behavior and dynamic recrystallization of near-eutectic Al–Si based alloys during hot compression

Highlights

• Flow stress of A8 alloy is more sensitive to the deformation temperature and strain rate.

• DRX of A8 alloy is significantly inhibited at relatively high strain rate (≥ 1 s⁻¹).

• The effect of micro-sized Si particles is corresponding to PSN.

• Nano-sized dispersoids exert dual effects on the present studied near eutectic Al–Si–Mg alloy at different deformation stages.

Abstract

Effect of trace addition of transition elements (Zr, V) on the flow behavior of near-eutectic Al–Si based alloys during hot compression was studied by Gleeble-3500 thermal simulator. Microstructure evolution was characterized by optical microscopy (OM), scanning electron microscope equipped with an electron backscattered diffraction (SEM/EBSD), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). Flow behavior shows that A8 alloy (with trace addition of Zr and V) is more sensitive to the deformation temperature and strain rate within a certain range. The activation energy of near-eutectic Al–Si alloy is greatly improved and dynamic recrystallization (DRX) is significantly inhibited at relatively high strain rate (≥ 1 s⁻¹), due to micro alloying of Zr and V. The DRX processes of both A3 (without addition of Zr and V) and A8 alloys are discussed, emphasizing on the joint effect of micro-sized Si particles and nano-sized dispersoids.

Introduction

Because of their excellent castability, high strength to weight ratio, low coefficient of thermal expansion, and good abrasion resistance [1], [2], [3], [4], Al–Si(–Cu)–Mg alloys have found wide application in automotive industry [5], [6], [7]. To facilitate their applications, their microstructure evolution and mechanical properties have been intensively investigated in this decade. It is noted that the focus of most of these studies is hot-extruded hypoeutectic Al–Si–Cu alloys [8], [9], [10], [11], with an aim to overcome their strength-ductility trade-off. An excellent strength-ductility combination (Yield strength (YS) ~ 311 MPa, ultimate tensile strength (UTS) ~ 398 MPa, and uniform elongation ~ 12.4%) was obtained in Al–6Si–2Cu–0.5Mg alloy processed by hot extrusion at 450 °C and subsequent T6 heat treatment [12]. Despite great progress, rare attention has been paid to the deformation behavior of near eutectic Al–Si–Mg alloys (which have a higher Si content than hypoeutectic Al–Si based alloys) since they are conventionally considered as casting alloys with poor deformation ability. However, a previous study shows that a greatly deformable Al–12Si–0.2Mg (wt%) alloy with an elongation of 15.0% can be obtained by a hot extrusion process with subsequent T6 treatment [13]. Moreover, minor addition of transition elements (Zr/V/Ti) can enhance the deformation ability of Al–Si–Mg alloys, even without subsequent T6 treatment [14], [15]. Specifically, the elongation of as-extruded Al–12.5Si–0.6Mg–0.075V (wt%) and Al–12.5Si–0.5Mg–0.1Ti (wt%) alloys were reported to be as large as 14.1% and 12.3%, respectively [14], [15]. All these studies indicate that an appropriate processing procedure can enhance the deformation ability of Al–Si(–Cu)–Mg alloys so that they have a great potential to be used as profiles. Therefore, in order to widen their application, it is significant to gain a deeper insight into the deformation behavior of Al–Si(–Cu)–Mg alloys.

Liao et al. [16] investigated the effect of Si amount on hot compression behavior and processing map of Al–Si–Mg alloys. Joseph et al. [17] examined the dependence of flow behavior on modification of a near eutectic Al–Si–Cu–Mg alloy in compression at strain rates varying from 3 × 10⁻⁴ to 10² s⁻¹ at three different temperatures (room temperature, 100 °C, and 200 °C). Shaha et al. [18] discussed the effect of Zr (0.20 wt%), V (0.25 wt%), and Ti (0.11 wt%) on hot compression behavior of Al–7Si–1Cu–0.5Mg (wt%) alloy. Although the deformation behavior of Al–Si based alloys has received some attention, these studies have been devoted to constructing constitutive equations and processing maps [19], [20], [21], [22], and rare work has been performed to simultaneously investigate the flow behavior and dynamic recrystallization (DRX) of near-eutectic Al–Si–Mg alloys with transition elements during hot compression.

In this paper, the effect of simultaneous addition of Zr and V on the flow behavior of near-eutectic Al–Si–Mg alloy during hot compression is studied. Meanwhile, the DRX processes of the Al alloy with large number of micro-sized eutectic Si particles and nano-sized particles are discussed. The micro-sized eutectic Si particles and nano-sized Zr/V/Ti-containing particles have completely different influence on the hot deformation behavior of Al alloys.