Monotonic and cyclic behaviour of cast and cast-forged AZ80 Mg

Abstract

Tensile and strain-controlled fatigue tests were performed to investigate the influence of forging on the performance of cast AZ80 magnesium alloy. The obtained microstructural analysis showed that the as-cast AZ80 magnesium alloy has dendritic α-Mg phase with eutectic Mg 17 Al 12 morphology and a random texture. In contrast, the forged samples showed refined grains and a strong basal texture. During tensile testing, a maximum yield and ultimate tensile strength of 182 MPa and 312 MPa were obtained for the forged samples, representing increases of 121% and 33%, respectively, from the as-cast condition. At the same time, a significant improvement (73%) in ductility was obtained in forged samples. It was also observed that the forged samples achieved comparatively longer fatigue life under strain-controlled cyclic loading. Analysis of the fracture surfaces showed that a cleavage-type morphology was typical for the ascast samples, while the occurrence of dimples and other evidence of plastic deformation were identified in the fracture surfaces of the forged specimens, indicating a more ductile response. Forging caused grain refinement and texture modification, both of which enhance alloy performance by improving strength and ductility, and leading to longer fatigue life. Strain and energy-based models were investigated for their suitability to predict the life of the forged material. Both the Smith-Watson Topper and the Jahed-Varvani energy-based models gave reliable life prediction.

Mg-Alloys for Forging Applications—A Review

“…Zinc is found solely in solid solution in AZ80. The microstructure of as-cast and forged AZ80 (which is further described in Reference [76]) is depicted in Figure 14. The micrographs show the coarse casting microstructure (Figure 14a) as well as recrystallized grains resulting from the forming tests, which were performed at varying temperatures and deformation rates.…”

“…The mechanical properties of forged AZ80 were analyzed by Gryguc et al [76,95]. Extruded and cast stock material was forged isothermally (375 • C and 20 mm s −1 ram speed) to a part shaped like an asymmetric I-crossbeam section, and the final parts were compared.…”

“…While the mechanical properties of the sample varied with texture and processing parameters, the extruded and forged material was found to be superior to the stock material in tensile tests as well as in LCF tests [95]. The same authors also investigated the mechanical behavior of as-cast and forged material (flatbread samples), which were formed isothermally in a temperature range of 350 to 450 • C at ram speeds of 0.65 mm s −1 and 6.5 mm s −1 [76]. It was found that the forging process significantly improved the properties of the cast material in the tested monotonic LCF and HCF (high cycle fatigue) regimes.…”

Characterization of the corrosion performances of as‐cast Mg–Al and Mg–Zn magnesium alloys with microarc oxidation coatings

“…Recently, intensive research and development work has been conducted in both academic and industrial institutes to develop advanced materials processing and surface treatment technologies for replacing aluminum using Mg alloys in the design and manufacture of fatigue‐critical automotive components, such as the control arm . Three grades of Mg alloy (i.e., AZ31B, AZ80, and ZK60) were selected as the candidate materials for the development of cost‐effective forging processes for the fabrication of a lower control arm, due to their superior mechanical properties and excellent forgeability . The corrosion properties of the bare Mg alloys substrate are determined by factors such as the alloy elements, phase composition, microstructure, processing history, and surface finish and so on …”

“…In the present work, the corrosion properties of as‐cast AZ31B, AZ80, and ZK60 alloys with and without MAO coatings have been investigated using advanced electrochemical and salt spray testing methods. The cast Mg alloys were used as the starting materials for development of the lower control arm . On the basis of the results of the corrosion properties of cast alloys, the corrosion and corrosion fatigue performances of the forged Mg alloys with and without coatings will be investigated in the follow‐up experiments.…”