Elsevier

Tribology International

Volume 46, Issue 1, February 2012, Pages 247-253
Tribology International

Friction behavior of laser cladding magnesium alloy against AISI 52100 steel

https://doi.org/10.1016/j.triboint.2011.06.030Get rights and content

Abstract

The use of magnesium alloys in engineering applications is becoming increasingly important as a relatively low density allows savings in energy consumption and therefore reduction in air pollution. An associated reduction in inertia makes these alloys potential candidates for friction components, but they suffer from poor wear resistance. Laser surface alloying with appropriate powder mixture is an innovative technique to improve surface properties of metallic alloys. In this study, the effect of laser surface alloying using Al12%Si powder on wear resistance of a magnesium alloy ZE41 is investigated. Hardness and wear resistance of the alloy are significantly enhanced after treatment.

Highlights

► Magnesium alloy ZE41 is modified by surface laser alloying with Al–Si powder. ► Mg2Si phases are created beneath the surface that increases hardness in the sub-layer. ► Increasing hardness close to the surface induces improvement of wear resistance. ► Wear resistance of treated ZE41 is 2.5 times higher than ZE41 in friction with steel.

Introduction

The need for weight reduction in the aircraft industry has raised interest in using magnesium alloys to replace aluminum alloys in some structural and mechanical parts. Indeed, magnesium alloy densities are 36% lower than aluminum alloys, leading to a high strength to weight ratio (180 kN m/kg, comparable with that achieved in aluminum alloys). Magnesium alloys are also attractive owing to their electromagnetic interference shielding properties and their recyclability. However, magnesium alloys present low hardness and wear resistance, and adhesion or seizing phenomena easily occur with the opposed materials, when friction is happening. One of the most effective ways to prevent an untimely adhesive and abrasive wear is to harden the surface.

In the previous years, the laser treatment was already employed to improve wear properties of titanium [1] and aluminum alloys [2]. However, the research in the field of laser surface treatment of magnesium alloys to prevent wear is limited and this field is still under development.

Galun et al. published one of the first contributions about the improvement of magnesium alloy wear properties by laser surface treatment. The authors have investigated the feasibility of laser surface alloying of some Mg base alloys with Al, Cu, Ni and Si and different combinations of these elements [3], [4]. In all cases the laser alloying process led to an increase of hardness caused by the formation of intermetallic compounds. This resulted in improved wear resistance and in some cases additionally in improved corrosion resistance.

Dutta Majumdar et al. have performed the laser surface alloying of MEZ1 magnesium alloy with SiC powder [5] or Al+Al2O3 [6] powders. In another work, the same authors studied the effect of a laser surface melting on wear resistance of the MEZ alloy [7].

Laser surface alloying of AZ912 with Si, SiC, TiC and Ni, (Al and Si) is reported to enhance sliding wear resistance of the alloy [8], [9], [10].

As can be seen, the studies on this subject are not numerous and often come from the same authors. In addition, most of the work concerned primarily with the process of surface treatment (laser parameters, injected powder, etc.). On surface properties, these studies compare mainly the wear loss of the as-received magnesium alloy and the same following laser surface modification. In most of cases, the superior wear behavior of laser surface modified layer is attributed to improved microhardness in the surface layer because of the presence of hard phases. The grain refinement in the treated area is also referred to as probable factor of improved wear resistance [7]. In these works, the authors provide little explanation of the wear mechanisms. Some point to the possibility that these mechanisms are complex and include adhesion, surface and abrasive wear [11].

In this investigation, the effect of laser surface alloying of commercial ZE41 magnesium alloy using Al12%Si powder on tribological properties is studied. A special effort is made to try to understand the mechanisms involved in friction and wear behavior.

Section snippets

Materials

The base material is a RZ5 commercial magnesium alloy (ASTM ZE41) produced by Honsel Foundry GMB, whose nominal composition is described in Table 1. Fig. 1 is a scanning electron micrograph of the microstructure of ZE41-T5. The micrograph shows an equiaxed grain structure of α-Mg consistent with cast plate, with a grain size about 50–150 μm. A second phase is clearly visible at the grain boundaries. It contains a main quantity of zinc and rare earths (RE: lanthanum and cerium) and has been

Coat structure

The coat is composed by five overlapping clads with a little more than 1.8 mm depth of penetration into the base material. The general coat macrostructure obtained is similar to the Al powder laser cladding of the same alloy described in [12]. There were no pores, either on the surface layer or at the interface between surface layer and base metal. The coat layer presents a very good bond aspect. The link between the deposited and the base alloy materials is a very solid and uniform one. Fig. 2

Conclusions

The microstructure and wear behavior of commercial alloy ZE41 modified by surface laser alloying with Al–Si powder mixture were studied. The coating is mainly composed of an Al–Mg matrix and dendrite precipitates of Mg2Si. Laser alloying process led to an increase of hardness with an improved microhardness, about 230 HV0.050, close to the surface, as compared to the 70 HV0.050 of the as-received substrate, caused by the formation of intermetallic compound Mg2Si.

The surface modification by laser

References (17)

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