Effects of precipitate and dendrite arm spacing on tensile properties and fracture behavior of As-Cast magnesium-aluminum alloys

Abstract

In the present study, the fracture behavior of Mg 17 Al 12 precipitate and the effect of dendrite arm spacing (DAS) on tensile properties of commercial as-cast AZ91D alloy were discussed. In order to obtain a wide range of DAS, the as-cast specimens were fabricated by various casting processes. With gravity-casting, the inoculation and various molds were utilized, and the solidification rates of melts were measured at four positions of the cone-type mold. The empirical equation between the solidification rate and DAS was found to be [DAS=82.2ε avg.]. Although the DAS as well as the grain size showed a Hall-Petch relationship with yield strength, the UTS and elongation indicated a parabolic relationship with respect to the variation of DAS. The fracture behavior of the as-cast AZ91D alloy was composed of three stages: (1) plasticity-induced crack initiation at the precipitate by matrix deformation, (2) crack growth through concentration of plastic deformation at the interface between the precipitate and matrix, and (3) agglomeration of cracks formed around the precipitate. The plasticity-induced crack is formed through severe deformation of the α-Mg matrix, and the size of the crack in the precipitate is limited by the thickness of the precipitate. Since the stress intensity level around the crack is lowered with the average diameter of the precipitate, the tensile properties of the ascast alloy could be enhanced by the decrease of the average diameter of the precipitate.

The microstructure, tensile properties, and creep behavior of AZ91, AS52 and TAS652 alloy

“…The use of microalloying addition for this purpose has attracted considerable attention for age hardening Mg-Sn based alloys [13]. However, the continuous network of Mg 17 Al 12 phases along the grain boundaries leads to intergranular fracture, such as AZ91D alloy [14]. The strength decreased with increasing test temperature, as expected.…”

Microstructure and Mechanical Properties of Face‐Centered‐Cubic‐Based Cr‐Free Equiatomic High‐Entropy Alloys

“…[ 34 ] The solute segregation‐induced strengthening by interaction with dislocations has been revealed in models. [ 82,83 ] Some researchers proposed that the yield strength abides by a Hall–Petch relationship with the DAS for cast alloys; [ 84,85 ] however, Hall–Petch relationship between yield strength and mean grain size, d , (, where k is the strengthening coefficient) has been more widely used in HEAs. [ 11,34,86 ] The grains of these HEAs in as‐cast state are very coarse with the average sizes >500 μm from the SEM images; the exact values of which were difficult to determine as the dendrites are stereoscopic in space.…”

Influence of As-cast Microstructure on Forging Behaviour of Magnesium Alloy AZ80

“…A similar study by Sharifi et al [41] showed an increase in flow stress in samples with a refined cast grain structure in AM60 and AZ91 at low levels of plastic strain. The tensile properties affected by dendrite arm spacing have also been thoroughly studied for magnesium-aluminum alloys and follow the Hall-Petch relationship with respect to increasing yield strength with decreasing grain size [42]. When comparing the effects of solidification rate and ageing on mechanical properties of AZ91, Cáceres et al [26] found no definitive correlation between solidification rate (and consequently the SDAS) and the room temperature yield strength or ductility of the material, though this is attributed to the dissolving of the γ-Mg 17 Al 12 particles, effectively erasing the dendritic structure.…”