Morphological Evolutions of Ni-Rich Phases in Al-Si Piston Alloys during 250–400 °C Thermal Exposure Processes

Haowei An,Haowei Wang,Jiwei Geng,Gen Liu,Dong Chen,Zeyu Bian,Mingliang Wang

doi:10.3390/ma13225212

Abstract

The thermal stability of the Al-Si alloys during the thermal exposure process from 250 °C to 400 °C was systematically investigated. The relationships between the morphological evolution and the mechanical changes of the alloys were determined through the Vickers hardness test and materials characterization method. Initially, the alloys exhibited similar thermal degradation behavior. For example, the exposure process of the alloy at 300 °C can be divided into two stages according to the changes of the alloy hardness and the matrix micro-hardness. In detail, the first stage (0–2 h) exhibited a severe reduction of the alloy hardness while the second stage showed a more leveled hardness during the following 98 h. There are three identified morphological characteristics of Ni-rich phases in the alloy. Furthermore, the differences in both composition and the micro-hardness between these Ni-rich phases were confirmed. The underlying relationships between the morphological transformation of the Ni-rich phases and hardness fluctuation in the alloy were correlated and elucidated. The observed alloy hardness increase when the exposure temperature was 400 °C was unexpected. This behavior was explained from the perspectives of both Ni-rich phases evolution and dispersoid formation.

Highlights

Al-Si alloys have been applied as heat-resistant Al alloys due to their excellent casting property and the interconnected eutectic Si structure [1,2,3]
The effect of thermal exposure (250–400 ◦ C) on the hardness of the Al-Si piston alloy has been analyzed based on the microstructure evolution during this process
Our work has systematically described and explained the Al-Si alloys thermal stability from the relationship between microstructure feature-mechanical property

Summary

Introduction

Al-Si alloys have been applied as heat-resistant Al alloys due to their excellent casting property and the interconnected eutectic Si structure [1,2,3]. The rigid Si network can bear more external load [4]. This eutectic Si phase tends to disintegrate and spheroidize when the alloy undergoes solution treatment or thermal exposure for a certain period of time, leading to a reduction of mechanical properties [5,6,7]. The alloying elements with lower solubility and diffusivity in the. This method aims to introduce some new heat-resistant phases into matrix

Results

Discussion

Conclusion