Constitutive Behavior of an AA4032 Piston Alloy with Cu and Er Additions upon High-Temperature Compressive Deformation

Suwaree Chankitmunkong,Dmitry G Eskin,Chaowalit Limmaneevichitr

doi:10.1007/s11661-019-05482-9

Abstract

Aluminum piston alloys of the AA4032 type are produced by direct-chill (DC) casting and subsequent forging; therefore, it is important to understand their thermomechanical behavior. In recent years, it was shown that additions of Cu and Er could improve mechanical properties of these alloys at room and high temperatures. In this work, we studied the constitutive behavior of AA4032-type alloys with and without Cu and Er additions. The experimental true stress–true strain curves were obtained by compression tests under various temperatures [683 K to 723 K (410 °C to 450 °C)] and strain rates (0.01 to 10 s−1) to determine constitutive parameters [strain-rate sensitivity, activation energy, and Zener–Hollomon (Z) parameter] for the hot deformation behavior of AA4032-type piston alloys with and without additions of Cu and Er. The flow stress decreased with increasing deformation temperature and decreasing strain rate. The results also showed that increasing the Cu content increased the flow stress over the applied range of deformation conditions due to solid-solution strengthening and the formation of primary Si particles, which led to an increase in the activation energy during hot deformation. Moreover, the main microstructural damage in the AA4032 alloy with 3.5 pct Cu was predominantly due to the cracking of primary Si particles. Additions of 0.4 pct Er and 3.5 pct Cu lower the activation energy of deformation, Q, as compared to the base alloy and the alloy with 3.5 pct Cu. The microstructures in the deformed specimens consisted of subgrains, recrystallized grains, and fine eutectic phases. The alloys containing Er demonstrated more polygonized grains at a low strain rate than the alloys without Er, indicating that Er hindered recrystallization development. The peak stress of the AA4032 alloy with 3.5 pct Cu alloy was higher than for the base AA4032 alloy and for the AA4032 alloy with 3.5 pct Cu and 0.4 pct Er additions, which was attributed to the prevalence of the work-hardening mechanism over the softening mechanism.

Highlights

ALUMINUM alloys are widely used in the automotive industry where light weight becomes important due to the introduction of electric vehicles and the neededManuscript submitted May 5, 2019
The results show that the flow stress increases with increasing the strain rate for all tested alloys, but the flow stress decreases as the temperature increases at a given strain rate (Figures 4 and 5)
Our experiments show that the flow stress and the peak stress increase with the Cu content in the alloy, while they decrease with Er addition

Summary

Introduction

ALUMINUM alloys are widely used in the automotive industry where light weight becomes important due to the introduction of electric vehicles and the neededManuscript submitted May 5, 2019. ALUMINUM alloys are widely used in the automotive industry where light weight becomes important due to the introduction of electric vehicles and the needed. Aluminum piston alloys are often used in engine parts that are exposed to high temperatures. The thermomechanical behavior of these alloys upon deformation becomes critical. There are limited reference data on the constitutive parameters that describe the thermomechanical behavior of high-silicon (near-eutectic) alloys. These constitutive parameters are important for computer simulations of alloy processing, which is useful for designing metal-forming processes, and for obtaining high-quality final products. There are two main mechanisms that occur in the microstructure during hot deformation. The first mechanism is work hardening, which results from dislocation generation and hindered

Methods

Results

Discussion

Conclusion