Materials Chemistry and Physics 124 (2010) 835–840 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Effect of roller burnishing on fatigue properties of the hot-rolled Mg–12Gd–3Y magnesium alloy P. Zhang a,b,∗ , J. Lindemann b , W.J. Ding a , C. Leyens c,d a National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiaotong University, Shanghai 200030, China b Chair of Physical Metallurgy and Materials Technology, Technical University of Brandenburg at Cottbus, Konrad-Wachsmann-Allee 17, 03046 Cottbus, Germany c Fraunhofer-Institut für Werkstoff- und Strahltechnik IWS, Winterbergstraße 28, 01277 Dresden, Germany d Institut für Werkstoffwissenschaft, Technische Universität Dresden, Helmholtzstraße 7, 01069 Dresden, Germany article info Article history: Received 4 November 2009 Received in revised form 8 July 2010 Accepted 27 July 2010 Keywords: Roller burnishing (RB) High cycle fatigue Magnesium alloy Mechanical surface treatments abstract Influence of roller burnishing (RB) on high cycle fatigue properties of the hot-rolled Mg–12Gd–3Y (wt.%) magnesium alloy was investigated. RB can significantly improve the fatigue life of the Mg–12Gd–3Y alloy. After RB, the fatigue strength (at 10 7 cycles) in the as-rolled alloy and the aging heat-treated (T5-treated) specimens increased from 150 and 155 MPa, to 225 and 210 MPa, respectively. RB led to a subsurface fatigue-crack nucleation in both the as-rolled and the T5-treated materials. In the as-rolled alloy, small cracks (in the stage I) propagated along cleavage planes after RB. In contrast, in the T5-treated specimens, the small cracks grew by coalescence of the sheared dimples. RB introduced a work-hardened case and compressive residual stresses in the near-surface region, which effectively retarded the fatigue-crack nucleation and/or propagation, leading to an improvement in fatigue life. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Magnesium alloys exhibit great potential to substitute alu- minium alloys in automotive industry for weight saving [1,2]. However, insufficient fatigue properties significantly restrict their applications [3,4]. Mechanical surface treatments such as shot peening (SP), roller burnishing (RB) and deep rolling (DR) can enhance the fatigue life of metallic materials [5–8]. Some investigations on the effect of mechanical surface treatments were performed on the Mg–Al alloys AZ31, AZ80 [9–12] and A8 [13], and also on the Mg–Zn–Zr alloy ZK60 most recently [14]. The results demonstrated that mechanical surface treatments effectively improved the fatigue properties of magnesium alloys [9–14]. Mg–Gd–Y magnesium alloys present not only a good creep resistance but also a high yield strength and reasonable elon- gation [15,16]. In the previous work [17], fatigue properties of Mg–12Gd–3Y alloy have been investigated. Consequently, a fatigue strength of about 150 MPa was observed, which was much higher than that of the wrought magnesium alloy AZ80 [11,17]. Aging heat-treatment (T5) improved fatigue life of the Mg–12Gd–3Y alloy slightly. The improvement in fatigue life of the Mg–12Gd–3Y ∗ Corresponding author at: Chair of Physical Metallurgy and Materials Technol- ogy, Technical University of Brandenburg at Cottbus, Konrad-Wachsmann-Allee 17, 03046 Cottbus, Germany. Tel.: +49 355 694383; fax: +49 355 692709. E-mail address: zhangp@tu-cottbus.de (P. Zhang). alloy by T5-treatement can be attributed to the precipitates, which retarded the crack nucleation [17]. Improvement of the fatigue strength of the Mg–12Gd–3Y alloy can further broaden its application fields. In the present work, the influence of RB on the surface characteristics and high cycle fatigue properties of the as-rolled Mg–12Gd–3Y alloy and the T5-treated specimens was studied. Particular emphasis was put on elucidating the effect of RB on the fatigue life, crack nucleation and propagation behaviours of the Mg–12Gd–3Y alloy. 2. Experimental The hot-rolled magnesium alloy Mg–12Gd–3Y (nominal composition in wt.%: 12 Gd, 3 Y, 0.5 Zr, balance Mg) was used in this work. Aging heat-treatment T5 was conducted at 225 ◦ C for 16 h in an oil bath oven, corresponding to the peak- aging of Mg–Gd–Y alloys [18]. Microstructure of the as-rolled Mg–12Gd–3Y alloy and the T5-treated specimens has been described in the previous work [17]. The as-rolled alloy consists of fine grains with an average grain size of about 30 m. Lots of particles with the size of about several m are located along grain boundaries. The particles identified by EDX are MgGdY intermetallic disperoids. The microstruc- ture of Mg–12Gd–3Y alloy after T5 aging treatment contained predominantly fine   precipitates [17]. The alloy was tested either at the as-rolled or the T5-treated conditions. Tensile tests were performed on threaded cylindrical specimens with a gauge length of 20 mm. The initial strain rate was 8.3 × 10 −4 s −1 . T5 heat-treatment improved the yield and tensile strengths of the Mg–12Gd–3Y alloy. The yield and tensile strengths increased from 250 and 362 MPa, to 275 and 436 MPa after T5 heat-treatment, respectively. However, T5-treatment is detrimental to ductility, the elongation decreases from 6.02% to 4.37%. The tensile properties of the Mg–Gd–Y alloy were described in detail in the previous work [17]. The hour-glass shaped round fatigue specimens (6 mm gauge diameter) were used for the fatigue tests. The S–N curves measured by using the electrolytically 0254-0584/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2010.07.070