Vliv korozního napadení na únavové chování hořčíkové slitiny AZ31

Influence of Corrosion Damage on Fatigue Behaviour of AZ31 Magnesium Alloy

abstrakt

en

The fatigue behaviour of bare and pre-corroded AZ31 magnesium alloy in the stress amplitude control mode was studied. Two sets of test specimens were exposed to corrosion environment prior to fatigue test. Corrosion of test specimens was carried out in a spray of neutral 5% solution of sodium chloride for period of 480 and 1000 hrs. In order to assess the corrosion rate and corrosion mechanism of experimental material, reference specimens were exposed to corrosion environment for period of time ranging from 1 to 1000 hrs. Fatigue tests in the stress amplitude control mode were carried out on smooth and pre-corroded specimens. Analysis of hysteresis curves was preformed. Comparison of cyclic deformation curves showed that cyclic deformation response is not affected by corrosion damage. Experimental data in both, the low and high cycle fatigue regions were fitted by means of regression functions. S-N curves exhibited smooth transition from the low to the high cycle fatigue regions. Presence of corrosion damage resulted in decrease in fatigue life by 23 % (480 hrs) and 42 % (1000 hrs) compared to the smooth specimens. Furthermore, metallographic and fractographic analysis were performed. In the smooth specimens, fatigue cracks initiated from the specimen surface or at inclusions. In the pre-corroded specimens, corrosion damage served as initiation site.

Bylo studováno únavové chování hladkých těles a těles po korozní degradaci ze slitiny AZ31 v módu řízené amplitudy napětí. Dvě série zkušebních vzorků byly vystaveny působení korozního prostředí před samotným únavovým zatěžováním. Koroze vzorku probíhala korozní komoře se solnou mlhou v neutrálním roztorku 5% NaCl po dobu 480 a 1000 hodin. Únavové zkoušky byly provedeny na hladkých a korodovaných tělesech v módu řízené apmlitudy napětí. Byla provedena nalýza hysterezních smyček, srovnání cyklických deformačních křivek ukázalo, že ceklická deformační odezva není ovlivněna korozním napadením. Experimentální data v nízko- a vysoko-cyklové únavové oblasti byla proložena regresní funkcí. Korozní napadení vedlo k poklesu únavové živtnosti o 23 % (480 hod.) a 42% (1000 hod.) ve srovnání s hladkými tělesy. Dále bylo provedeno metalografické a fraktografické hodnocení. na hladkých tělelesech iniciovaly únavové trhliny na povrchu, případně na inkluzích, u korodovaných těles docházelo k iniciaci únavových trhlin na lokálním korozním napadení.

The fatigue behaviour of bare and pre-corroded AZ31 magnesium alloy in the stress amplitude control mode was studied. Two sets of test specimens were exposed to corrosion environment prior to fatigue test. Corrosion of test specimens was carried out in a spray of neutral 5% solution of sodium chloride for period of 480 and 1000 hrs. In order to assess the corrosion rate and corrosion mechanism of experimental material, reference specimens were exposed to corrosion environment for period of time ranging from 1 to 1000 hrs. Fatigue tests in the stress amplitude control mode were carried out on smooth and pre-corroded specimens. Analysis of hysteresis curves was preformed. Comparison of cyclic deformation curves showed that cyclic deformation response is not affected by corrosion damage. Experimental data in both, the low and high cycle fatigue regions were fitted by means of regression functions. S-N curves exhibited smooth transition from the low to the high cycle fatigue regions. Presence of corrosion damage resulted in decrease in fatigue life by 23 % (480 hrs) and 42 % (1000 hrs) compared to the smooth specimens. Furthermore, metallographic and fractographic analysis were performed. In the smooth specimens, fatigue cracks initiated from the specimen surface or at inclusions. In the pre-corroded specimens, corrosion damage served as initiation site.

hořčíková slitiny, koroze, únava

magnesium alloy, corrosion, fatigue

21.05.2013

Magnesium Workshop Madrid 2013

25–25