The low cycle fatigue behavior of aluminum alloy based particulate composites

MB85 (Al-3.5%Cu-2.4%Mg Alloy reinforced with SiC particulates) and 2014 (Al-4.2%Cu-1.5%Mg alloy reinforced with Al₂O₃ particulate) composites were heat-teated to underaged and overaged conditions followed by low cycle fatigue testing with total strain control. The results include three aspects: (i) Bauschinger effect and internal residual stress, (ii) Cyclic work hardening behavior, and (iii) Fatigue life and low cycle fatigue damage processes. X-ray diffraction techniques were used to measure the residual internal stress to compare with the Bauschinger measurements. SEM and TEM were used to characterize the microstructures before, during, and after the test. In light of a literature review on the above aspects, the possible mechanisms occuring during cyclic deformation and fatigue are discussed. The main results are as follows:

(1) Bauschinger parameters (σ_b and β¹) increase with increasing plastic prestrain (ε_p).

(2) Reinforcements and heat treatment conditions have strong effects on the BEPs: BEP_OA > BEP_UA in the same material; BEP_CP > BEP_CT in the same heat treatment; BEP_20%SiC > BEP_15%SiC in the same heat treatment.

(3) Internal stress may be measured both by Bauschinger Effect and by x-ray diffraction. Both results are comparable.

(4) Cyclic deformation behavior is strongly affected by the reinforcements and heat treatment conditions. For a given composite material and a fixed heat treatment condition, the cyclic deformation behaviors is determined by the initial plastic strain.

(5) The Manson-Coffin expression can be used to predict the fatigue life of the composites.