Impact of surface treatment and surface condition on fatigue and fracture resistance of materials in hot forging of aluminum alloy parts

Introduction

High-performance steels have multiple applications; they are frequently used in tools for the manufacture of aluminium alloy parts, for instance, injection moulds, extrusion and stamping tools, or in forging dies. These materials provide high mechanical strength and high wear resistance during high-temperature operation. Their heat treatment determines the compromise between fracture toughness and hardness for each application. Thus, the degree of quenching and tempering is frequently selected based on these parameters. However, the mechanical durability of these materials is very sensitive to their surface condition and contact with potentially corrosive fluids. On the other hand, in the case of aluminium parts manufactured by this process, the use of surface treatments is very common in improving the finished component's performance. These treatments may or may not point to improvement in mechanical durability. Nevertheless, they can be a determining factor on the fatigue resistance of the manufactured component.

Methods

For this work, the effect of the surface state, the contact with operational fluids, and different surface treatments on fatigue resistance has been studied experimentally. The fundamental materials of the hot forging process, both the high-performance steels used for the dies, and the aluminium alloys of the manufactured components, have been studied. Surface modification treatments such as shot peening and anodisation have been tested, and their influence on the mechanical durability was assessed.

Results and conclusions

The results of this work confirm the sensitivity of fatigue resistance, both in low-cycle and high-cycle regimes, for high-performance steels when exposed to aggressive environments that can generate surface corrosion. Likewise, the behaviours of high-strength aluminium alloys, when subjected to surface finishing treatments for increasing mechanical durability and corrosion resistance, such as shot peening and anodisation, respectively, are presented.