بررسي خواص مكانيكي و عمر خستگي ورقهاي آلومينيوم 5083 حاصل از فرايند نورد در كانال‌هاي همسان زاويه‌دار (ECAR)

Investigation of mechanical properties and fatigue life of Al-5083 sheets processed by equal channel angular rolling

در اين نوشتار اثرات فرايند نورد در كانال‌هاي همسان زاويه‌دار (ECAR) بر خواص مكانيكي و عمر خستگي ورق‌هاي حاصل از اين فرايند بررسي شده است. بدين منظور ابتدا ورق‌هاي آلومينيومي Al-5083 توليد شده طي اين فرايند تحت آزمون‌هاي مكانيكي مختلف ــ نظير كشش، سختي و خستگي كششي ــ قرار گرفتند. بررسي‌هاي خستگي براساس روش كرنش پايه با دامنه‌ي كرنش ثابت، فركانس 5/0 هرتز و نسبت كرنش 75/0 انجام شده است. تمامي آزمون‌ها در محيط استاندارد آزمايشگاهي انجام شده، و نتايج حاصله حاكي از افزايش استحكام كششي نمونه با سه بار عبور از قالب تا حدود 2 برابر نمونه‌ي آنيل شده‌ي اوليه است؛ اين افزايش استحكام كششي با كاهش ازدياد طول نمونه همراه بوده است. سختي ورق‌ها نيز به‌طور پيوسته با افزايش تعداد عبورها بيشتر مي‌شود. نتايج آزمون خستگي نشان مي‌دهد كه عمر خستگي در محدوده‌ي زير 5 10 چرخه با افزايش تعداد عبورها مرتباً كاهش مي‌يابد.

Equal Channel Angular Rolling (ECAR) is a continuous severe plastic deformation process. In this process, severe shear strains are applied to the sheet. This strain increases the yield or ultimate strength of sheet without significant change in sheet dimension. In this article, the effect of ECAR process on mechanical properties and fatigue life of manufactured sheets will be studied. Four Al-5083 samples have been prepared and annealed for obtaining stress-free samples. Three samples have been rolled by ECAR process with 1, 2, and 3 pass of rolling, respectively. Mechanical tests including tensile test, hardness, and axial fatigue tests have been carried out on prepared samples. Fatigue tests have been implemented according to strain-based approach with constant strain ratio and 0.5 Hz frequency of loading. Strain ratio (ratio of minimum strain to maximum strain in each cycle) is selected which equals 0.75. All of the tests have been carried out in a controlled laboratory condition. Fatigue life of samples is defined as the total of cycles before complete rupture of samples. Results show that the ultimate tensile strength (UTS) of samples increases with increasing the pass of rolling. Also, the maximum elongation of samples decreases. Maximum elongation was 17% in annealed sample, while it decreases to 10% in sample with three pass of rolling. The hardness of samples has been measured by Vickers micro harness test. The hardness of samples increases at higher pass of rolling. Fatigue test results show that fatigue life of Al-5083 samples decreases in manufactured sheets of equal channel angular rolling process.