Lubomír Čížek

Influence of Heat Treatment on Structure and Properties of the Cast Magnesium Alloys

In this paper is presented the structure and proprieties of the cast magnesium alloys as cast state and after heat treatment cooled with different cooling rate, depending on the cooling medium (furnace, water, air). For investigations samples in shape of 250x150x25 mm plates were used. The presented results concern X-ray qualitative and quantitative microanalysis as well as qualitative and quantitative X-ray diffraction method, tensile tests, hardness measurement. In the analysed alloys a structure of α %solid solution and fragile phase β (Mg17Al12) occurred mainly on grain borders as well as eutectic and phase AlMnFe, Mg2Si. Investigation are carried out for the reason of chemical composition influence and precipitation processes influence to the structure and mechanical properties of the magnesium cast alloys with different chemical composition in as cast alloys and after heat treatment.

Metallographic Analysis of ECAP Processed Selected Magnesium Alloys

Magnesium alloys has been used for a wide variety of applications, namely from the reason of their low density and high strength–to–weight ratio. The properties of magnesium alloys are connected with microstructure that is influenced by metallurgical and technological aspects. Scope of utilisation of foundry magnesium alloys is continuously being extended, so if we want to operate as competitive producers, it is necessary to investigate very actively properties of individual alloys, optimise their chemical composition, study issues of their metallurgical preparation, verify experimentally their casting properties and conditions of successful casting of castings by individual methods, including heat treatment. Recently, however, increases also utilisation of formed magnesium alloys namely application of SPD methods. The experimental part deals with hardness and structure determination of selected magnesium alloys after ECAP processing.

The Influence of Severe Plastic Deformation Process on Structure and Properties of AZ 31 Alloy after Selected Heat Treatment

The technology of structure refinement in materials with the aim of achieving substantial mechanical properties and maintaining the required plasticity level is becoming increasingly useful in industrial practice. Magnesium alloys are very progressive materials for utilization in practice thanks to their high strength-to-weight ratios (tensile strength/density). The presented paper analyses the effect of the input heat treatment of the AZ31 alloy on the change of structure and strength properties through the process of severe plastic deformation (SPD), which finds an increasing utilization, especially in the automotive and aviation industry. For the study of the influence of the SPD process (ECAP method) on the properties of the AZ31 alloy, two types of thermal treatment of the initial state of the structure were selected. The analysis of the structure of the AZ31 alloy was performed in the initial state without heat treatment and subsequently after heat treatment. In the next part, the influence of the number of passes on the strengthening curves was evaluated. Mechanical properties of the AZ31 alloy after ECAP were evaluated by hardness measurement and completed by structure analysis.

Grain Refinement of AZ61 Alloy after ECAP Processing

Electron microscopy techniques were used to characterize the microstructure and deformation behavior of AZ61 alloy proceeded by ECAP. The commercial AZ61 alloy subjected to severe plastic deformation possesses a two-phase microstructure consisting of solid solution matrix and massive γ-phase Mg17Al12, or Mg17(Al,Zn)12 distributed mostly at grain boundaries. Based on selected area diffraction and electron back scattered diffraction applied to a sample after the third pass, it can be concluded that plastic deformation induced by ECAP occurs mainly by slip mode forming a high density network of dislocation inside the grains. The grains size was significantly refined to 1.4 μm after the third pass of ECAP. The refinement of grain size is probably due to polygonization process associated with formation of high angle grain boundaries due to dislocations rearrangement. (Al, Zn)12Mg17 precipitates of size scattered from 100 to 200 nm and also the primary precipitates of Al6Mn phase were observed in this alloy.