Notch Size Effects in the Fatigue Characteristics of Al-Si-Cu-Mg Cast Alloy

Abstract

Influences of the microstructure, micro defects and the stress concentration factor on fatigue characteristics were investigated for a JIS-AC4B alloy containing 6.79%Si, 2.93%Cu, 0.17%Mg and 0.59%Fe, and for an iron free Al-Si-Cu-Mg alloy. Solidification microstructures consist of dendritic phase, eutectic Si, Al 2 Cu and Mg 2 Si phases in both alloy specimens and a few gas and shrinkage porosities appear in every specimen; while Fe compound modified by Mn appears among the dendrites in the AC4B alloy. Rotating bending fatigue tests were carried out on specimens with notches of 2, 1, 0.3 and 0.1 mm radius. Both AC4B and Al-Si-Cu-Mg alloys show the same fatigue sequence when the notch size is larger than 1 mm, indicating that the gas and shrinkage porosities act as the origins of cracking and thus govern the fatigue characteristics. Contrarily, when the notch radius becomes smaller than 0.3 mm, so that the stress concentration factor becomes larger than 2.4, the AC4B alloy has a higher fatigue strength than the Al-Si-Cu-Mg alloy, indicating that Fe-compounds may retard crack propagation.

Elevated temperature low cycle fatigue of a gravity casting Al–Si–Cu alloy used for engine cylinder heads

“…Most previous work on the fatigue properties of Al-Si-Cu alloys has been done in trying to understand the interaction between the fatigue loading and microstructural features. In particular, the fatigue behaviors of Al-Si-Cu alloys were controlled by factors such as dimension and shape of shrinkages/pores [2,3,4], SDAS (secondary dendrite arm spacing) values [2,5], as well as presence of Fe-based intermetallic phases (the chinese-script-like Į-Al 15 (Fe,Mn) 3 Si 2 phase and needle-like ȕ-Al 5 FeSi phase) [6]. Among those, porosity caused a significant deterioration of the fatigue properties for Al-Si-Cu alloys [7,8].…”

“…Therefore, strain-controlled low cycle fatigue (LCF) is a major cause of damage that, eventually, leads to the failure of engine parts exposed to high temperatures. However, most published works on ϰ Al-Si-Cu alloys have been focused on the stress controlled high cycle fatigue (HCF) regime [3][4][5][7][8][9][10][11][12][13]15]. Only a few strain controlled LCF studies are available on Al-Si-Cu alloys [14,[17][18][19][20].…”

Influence of Solidification Microstructure and Distribution of Reinforcement on Fatigue Characteristics of Notched SiC Reinforced AC4B Alloy Composites

“…It is generally recognized that experimental results for fatigue tests on notch-free specimens are significantly scattered, since there are differences in stress distribution and concentration in specimens even at the same nominal stresses, due to different internal cast defects, sizes, shapes and positions. [18][19][20][21] Therefore, the amount and size of the porosity were investigated, and both parameters were found to be higher in the composites, as shown in Table 2. Hence, the increase in the volume fraction of porosity could be one of the reasons for the decline in the fatigue strength.…”