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2 Zeszyty Naukowe. Mechanika / Politechnika Opolska

2 2010

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Effect of heat treatment on mechanical properties of magnesium alloy AZ61

Dolezal P., Zapletal J., Gejdos P.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

2010

z. 97

49-50

The contribution is focussed on the assessment of the influence of a heat treatment of magnesium alloy AZ61 on its mechanical properties. The magnesium alloy AZ61 was manufactured by squeeze casting method using alternative two-stage casting. Metallographic analysis was made by means of light and electron microscopy utilising also the possibility of local chemical analyses. The assessment of the influence of a heat treatment on mechanical properties of AZ61 magnesium alloy was performed by means of tensile tests on specimens of rational geometry. The heat treatment of the bars was performed at the temperature of 380 °C and with dwell from 1 to 16 hours to result in T4 (solution annealed) state. Basic stress and strain characteristics were assessed from the results of the tensile tests. It follows from the experimental results that the tensile strength and deformation characteristics grow even after only 1 hour of dwell at the temperature of 380 °C. Maximum values of tensile strength and deformation characteristics were achieved after 6 hour dwell at the temperature. It was confirmed by the metallographic analysis of the test specimens that there occurs the dissolution of the hard and brittle Mg17Al12 intermetallic phase. It was found by the local chemical analysis that the decrease in micro-heterogeneity of the ä solid solution takes place here at the same time. The increase in the tensile strength and deformation characteristics is caused by the dissolution of the hard and brittle intermetallic phase and by the decrease in heterogeneity of the matrix.

Effect of heat treatment on chemical and microstructural heterogeneity of magnesium alloy AZ61

Horynova M., Dolezal P., Janova D., Gejdos P.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

2010

z. 97

51-52

The contribution is focussed on the assessment of the influence of a heat treatment of magnesium alloy AZ61 on its chemical and microstructural heterogeneity. The experimental material was manufactured by squeeze casting method using alternative two-stage casting. The microstructure of the alloy in as cast state composed of ä solid solution, Mg17Al12 intermetallic phase and minor phases based on Mn. The heat treatment applied on the alloy was the solution annealing at the temperature of 380 °C and with graded dwell from 1 to 8 hours. Chemical etching was employed in order to estimate the micro-segregation of the elements in the matrix qualitatively and to discern the phases in the microstructure. The differences in matrix heterogeneity between the as cast state and after annealing were documented by means of light microscopy. Differences in etching between the central part and periphery of the crystalline units are apparent in the metallographic images. Quantitative assessment of chemical heterogeneity was done by mapping and local chemical microanalyses. It was found by mapping that with increasing delay at annealing temperature the Mg17Al12 intermetallic phase gradually dissolves and the micro-heterogeneity of each element decreases. Chemical heterogeneity of particular elements was measured by local chemical analysis and the intensity of chemical micro-heterogeneity of each sample was further expressed using effective distributive coefficients. It follows from the results that the solution treatment of the AZ61 magnesium alloy leads to diminishment of the chemical and microstructural heterogeneity. It also follows from the results presented that the combination of metallographic analyses with X-ray spectral analysis of wave- or energy-dispersive type is advantageous for the quantitative assessment of micro-segregation of elements in the matrix of magnesium alloys.