Únavová odolnost hořčíkové slitiny AZ91

CYCLIC FATIGUE RESISTANCE OF AZ91 MAGNESIUM ALLOY

journal article - other

en

The paper deals with 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 determined by static tensile test. Furthermore, fatigue parameters were investigated. 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 fitting with suitable regression functions (Kohout & Věchet and Stromeyer) for determination of the fatigue parameters. Fatigue limit ?C of the studied alloy for 108 cycles is approaching 50 MPa. In addition, the fracture surfaces were observed by scanning electron microscopy. The failure analysis proved that the striations were observed in fatigue crack propagation area and in the area of static fracture was observed the transgranular ductile fracture. The 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. Na hladkých zkušebních tělesech při symetrickém namáhání tah-tlak za normální teploty byla naměřena Wöhlerova-Basquinova závislost a 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. Fraktografická analýza prokázala, že se striace vyskytují v oblasti šíření trhliny a v oblasti statického dolomu byl pozorován transkrystalický tvárný lom. Struktura studované slitiny v základním stavu a po tepelném zpracování byla pozorována světelným a rastrovacím elektronovým mikroskopem.

The paper deals with 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 determined by static tensile test. Furthermore, fatigue parameters were investigated. 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 fitting with suitable regression functions (Kohout & Věchet and Stromeyer) for determination of the fatigue parameters. Fatigue limit ?C of the studied alloy for 108 cycles is approaching 50 MPa. In addition, the fracture surfaces were observed by scanning electron microscopy. The failure analysis proved that the striations were observed in fatigue crack propagation area and in the area of static fracture was observed the transgranular ductile fracture. The structure of the studied alloy in the basic state and after heat treatment was observed by light and scanning electron microscopy.

Hořčíková slitina, rozpouštěcí žíhání, mechanické vlastnosti, únavové chování, fraktografie

Magnesium alloy, solution annealing, mechanical properties, fatigue properties, fractography

2009

09.11.2009

Žilina

1335-0803

Materiálové inžinierstvo

XVI

4/2009

5–10

6