Papers by Keyword: AZ91 Alloy

Abstract: Specimens of rectangular and circular cross section of a Mg-9Al binary alloy have been tensile tested and the cross section of undeformed specimens examined using scanning electron microscopy. The rectangular cross sections showed three scales in the cellular intermetallics network: coarse at the core, fine at the surface and very fine at the corners, whereas the circular ones showed only two, coarse at the core and fine at the surface. The specimens of rectangular cross section exhibited higher yield strength in comparison to the circular ones. Possible reasons for the observed increased strength of the rectangular sections are discussed.

Abstract: This paper presents a study of the residual strain field within a high pressure die cast (HPDC) AZ91 Mg alloy bar subjected to four point bending. The technique employed for this purpose is high energy synchrotron X-ray diffraction. Strain scanning using polychromatic X-ray beam allows the collection of multiple peak diffraction patterns and monitoring of small peak shifts as a function of beam position. These shifts allow collective interpretation in terms of the equivalent macroscopic residual elastic strain. Residual elastic strain distributions were studied in the sections subjected to pure bending and also in sections of contact between the sample and the rollers. These experimental results are compared with the predictions from a finite element analysis of contact and deformation. Good agreement is found between the modelled and measured results. It is hoped that these results help improved understanding of complex deformation behaviour of thin-walled HPDC AZ91 components and provide useful background information for lifing assessment of such structures.

Abstract: In this paper, the solution mainly containing Zn(H2PO4)2 was used to prepare phosphating coatings on AZ31,AZ61 and AZ91 magnesium alloys. The effects of the phosphating parameters and the composition of phosphating solution on the formation of the coatings were investigated by orthogonal tests. The corrosion behaviors of the phosphating coatings were also studied and it is found that there was no hydrogen evolution in at least 1h. In the last, 60~80μm organic coatings were painted on the phosphated magnesium alloys,the organic coatings adhered to the phosphating coating, and the anti-corrosion abilities were improved .

Abstract: The corrosion of AZ91 magnesium alloy with residual stress was observed in-situ in an atmosphere of water vapor with cyclic wet-dry conditions using environmental scanning electron microscope (ESEM). The results showed that the oxygen concentration on the surface generally increased with the wetting time. And the average corrosion rate of AZ91 alloy with residual stress (RS) was much larger than that without RS, indicating RS accelerated corrosion. The corrosion localized at primary α-Mg area at short wetting time, but with the increase of wetting time spread to the eutectic α-Mg region. Small-size as-cast defects (<50μm) contributed little to the average corrosion rate while large-size as-cast defects (>100μm) influenced the distribution of water film and corrosion on the surface.

Abstract: Mg is the lightest structural metal with the highest specific strength. It is therefore considered as a solution for vehicular mass reduction so as to reduce the fuel consumption and greenhouse gas emission. Unfortunately, Mg and its alloys are highly susceptible to corrosion, particularly in salt-spray conditions. This has limited its use in the automotive and aerospace industries, where exposure to harsh service conditions is unavoidable. To improve its corrosion resistance it is viable to apply a desirable engineering coating on the Mg surface.This communication discusses the practical aspects of magnesium surface modification based on our review. A novel immersion coating process is also discussed along with the corrosion behavior of coated and uncoated AZ91 magnesium alloy.

Abstract: Nickel foam reinforced AZ91 magnesium alloy was fabricated by using melt infiltration and water quenching methods. The mechanical properties were measured in compressive and tensile deformation modes. Fracture surfaces were examined by scanning electronic microscopy. The results show that addition of nickel foam results in a significant increase in elastic modulus, yield strength of the composite material. However, ductility of the composite was adversely affected when compared to the unreinforced monolithic counterpart.

Abstract: The infiltration pressure field of fiber reinforced AZ91D was studied in this paper. The carbon fiber T300 was selected and covered with rough TiO2 coat by means of plasma techniques. These carbon fibers were combined together and a kind of continuous pre-former with many micro-passes was constructed. When this pre-former went though a infiltration cabin filled with molten magnesium alloys, the melt infiltrated into pre-former through those micro-passes under infiltration pressure. A physical model and related mathematic model were built to relate this process. The relationship among pressure (p), infiltration flow rate change (e) and the location of infiltration flow (r) was molded.

Abstract: The effect of second phase on the mechanical properties of AZ61 and AZ91 Mg-Al-Zn magnesium alloy processed by equal-channel angular extrusion (ECAE) has been investigated. The results revealed that cracks initiated at and propagated through the α-Mg/β-Mg17Al12 interfaces and grain boundaries of Mg-Al-Zn alloys during tensile deformation. For AZ61, the elongation increased with the increase of ECAE pass number and the decrease of grain size. However, the elongation of AZ91 with more second phase particles decreased with the increase of ECAE pass number and the decrease of grain size.

Abstract: In present work, Si and Sr elements were added into AZ91 alloy and cast directly into test samples using permanent mold. Mechanical properties of the samples at room temperature were evaluated by tensile test and the microstructure was analyzed. The results show that β-phase (Mg17Al12) of AZ91 alloy decreases with the addition of Si element and Mg2Si phase forms at the same time. Irregular Mg2Si phase precipitates preferentially at the grain boundaries at a low silicon content level. With the increase of the Si content, Mg2Si phase shows a complicated “Chinese- script” shape distributed at the grain boundary which leads to a lower ultimate tensile strength. Subsequently, the addition of Sr element has a remarkable effect on the form and distribution of Mg2Si phase of AZ91-Si alloys.

Abstract: The microstructures and corrosion properties of AZ91 magnesium alloy with trace additions of Sc were investigated. The microstructures were observed by OM and SEM, and the corrosion properties were studied by electrochemical technique. The results show that the alloys with Sc form a second-phase Al3Sc, the grains become finer with the increasing content of Sc and the microstructure is the finest when Sc content up to 0.6%, the corrosion resistant of alloy combining with Sc is improved.