Abstract

Designers’ efforts to use the lightest possible materials with very good mechanical properties mean that in recent years magnesium alloys have been increasingly used. It is well-known that the use of various plastic working processes allows achieving even better strength properties of the material, often without significant loss of plastic properties in relation to the properties of products obtained in the casting process. The article presents the results of research on microstructural changes and mechanical properties of the alloy AZ91 (MgAl9Zn1) occurring in samples subjected to conventional plastic deformation and the KOBO method. The obtained results were compared to the properties of reference samples, i.e., cast samples. The article presents the advantage of using the low-temperature KOBO method compared to the high-temperature deformation in a conventional manner. Moreover, it has been shown that the use of KOBO extrusion allows the alloy AZ91 (MgAl9Zn1) to obtain superplasticity properties with an elongation of up to 577% compared to the cast reference sample, which is generally classified as difficult for plastic deformation.

Highlights

  • In recent years, the use of magnesium alloys as construction materials has become more and more popular

  • The KOBO method was used during research on plastic deformation of hard-to-deform materials, including: MMC (Metal Matrix Composite), aluminum alloys (7075), titanium, bronze (CuSn8), magnesium alloys (AZ31 (MgAl3Zn1), AZ91 (MgAl9Zn1), AZ61 (MgAl6Zn1)) [36,37,38], and compared to the results obtained for typical plastic forming processes, such as extrusion, pressing, forging, rolling or drawing [39,40]

  • It is within the range typical for magnesium alloys with superplastic properties (0.3–0.6), which allows to strengthen the thesis about superplasticity of the alloy produced, which by nature is not intended for plastic working

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Summary

Introduction

The use of magnesium alloys as construction materials has become more and more popular. According to the appropriate procedure accompanying the application of the KOBO method to plastic working processes, it is possible to carry out “cold” (i.e., below the recrystallization conditions of a given material) plastic forming processes with a speed and degree of processing much higher than in high-temperature processes, and the product obtains a fine-grained, homogeneous structure and favorable mechanical properties [30]. The KOBO method was used during research on plastic deformation of hard-to-deform materials, including: MMC (Metal Matrix Composite), aluminum alloys (7075), titanium, bronze (CuSn8), magnesium alloys (AZ31 (MgAl3Zn1), AZ91 (MgAl9Zn1), AZ61 (MgAl6Zn1)) [36,37,38], and compared to the results obtained for typical plastic forming processes, such as extrusion, pressing, forging, rolling or drawing [39,40]. In order to verify whether the cast magnesium alloy AZ91 (MgAl9Zn1) subjected to plastic deformation could exhibit superplastic properties, tensile tests were carried out at the temperature of 300 ◦C and 350 ◦C

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