ÚNAVOVÉ VLASTNOSTI HOŘČÍKOVÉ SLITINY AZ91

FATIGUE BEHAVIOUR OF AZ91 MAGNESIUM ALLOY

journal article - other

en

The paper deals with the determination of principal mechanical properties and the investigation of fatigue behaviour of AZ91 magnesium alloy. The experimental material was made by squeeze casting technique and heat treated to obtain T4 state (solution annealing), when hard, brittle Mg17Al12 intermetallic phase is dissolved. The basic mechanical properties (Young's modulus, ultimate tensile strength, yield strength, elongation to fracture and reduction of area) were determinated by static tensile test. Furthermore, fatigue parameters were investigated and standard tensile curve was compared with cyclic stress-strain curve. The comparison indicates that studied material exhibited cyclic hardening at whole lifetime. In addition, the S-N curve on the basis of smooth test bars tested under symmetrical push-pull loading at room temperature was evaluated. The measured data were subsequently used for assessing the Manson-Coffin curve and for fitting with suitable regression function for determination of the fatigue parameters. Fatigue limit ?C of the studied alloy for 108 cycles is approaching 50 MPa. Structure of the studied alloy in the basic state and after heat treatment was observed by light and scanning electron microscopy.

Tato práce je zaměřena na stanovení základních mechanických charakteristik a zkoumání únavového chování slitiny hořčíku AZ91. Studovaná slitina byla vyrobena metodou squeeze casting a tepelně zpracována na stav T4 (tj. rozpouštěcí žíhání), které způsobuje rozpouštění tvrdé, křehké intermetalické fáze Mg17Al12. Byla provedena statická zkouška tahem a stanoveny napěťové a deformační charakteristiky (modul pružnosti, mez pevnosti, mez kluzu, tažnost a kontrakce). Dále bylo provedeno měření únavových parametrů a srovnána jednosměrná tahová křivka s cyklickou deformační křivkou. Z tohoto srovnání vyplynulo, že studovaný materiál cyklicky zpevňuje. Na hladkých zkušebních tělesech při symetrickém namáhání tah-tlak za normální teploty byla naměřena Wöhlerova-Basquinova závislost a odvozená Mansonova-Coffinova křivka zkoumaného materiálu. Experimentálně naměřená data byla proložena vhodnou regresní funkcí a stanoveny únavové parametry. Mez únavy ?C studované slitiny pro hladká zkušební tělesa určená pro 108 cyklů se blíží 50 MPa. Struktura studované slitiny v základním stavu a po tepelném zpracování byla pozorována světelným a rastrovacím elektronovým mikroskopem.

The paper deals with the determination of principal mechanical properties and the investigation of fatigue behaviour of AZ91 magnesium alloy. The experimental material was made by squeeze casting technique and heat treated to obtain T4 state (solution annealing), when hard, brittle Mg17Al12 intermetallic phase is dissolved. The basic mechanical properties (Young's modulus, ultimate tensile strength, yield strength, elongation to fracture and reduction of area) were determinated by static tensile test. Furthermore, fatigue parameters were investigated and standard tensile curve was compared with cyclic stress-strain curve. The comparison indicates that studied material exhibited cyclic hardening at whole lifetime. In addition, the S-N curve on the basis of smooth test bars tested under symmetrical push-pull loading at room temperature was evaluated. The measured data were subsequently used for assessing the Manson-Coffin curve and for fitting with suitable regression function for determination of the fatigue parameters. Fatigue limit ?C of the studied alloy for 108 cycles is approaching 50 MPa. Structure of the studied alloy in the basic state and after heat treatment was observed by light and scanning electron microscopy.

Únava, slinina hořčíku, rozpouštěcí žíhání, mechanické vlastnosti

Fatigue, magnesium alloy, solution annealing, mechanical properties

2009

01.12.2009

1210-0471

Transaction of the VŠB-Technical university of Ostrava, Mechanical series

2009

3

141–147

7