Deformation Behaviour Of Mg-6Al-3Sn Alloy As Well As Its Microstructure And Mechanical Properties After Hard-plate Rolling

Magnesium (Mg) alloys have enormous potential for applications in the aerospace,automotive and automobile industries, due to their outstanding properties such as low density,high specific strength and easy recovery. However, the developments of wrought Mg alloysare really hindered for their limited room temperature formability and strong anisotropy.Solving these problems needs a better understanding of the deformation mechanisms of Mgalloy. In this paper, we investigated the microstructure evolution and mechanical behavior ofnew Mg–6Al–3Sn (AT63) Mg alloys, during uniaxial deformations and plane straincompressions (PSC). The focus was on the twinning and dislocation slip mechanisms. Basedon the plastic theory of Mg alloy under various strain modes, we proposed an innovativerolling approach, i.e., hard-plate rolling. The main conclusions can be summarized asfollows:(1) Uniaxial compressions were carried out on an extruded AT63Mg alloy plate with dualbasal texture. Due to the dual basal texture, this plate exhibited a coexistence ofextension and contraction twinning. It was found that orthogonal texture componentsresulted in both extension and contraction twins during the compressions along theextrusion direction (ED), transverse direction (TD) and normal direction (ND). Thisresult is helpful for the texture design to reduce the mechanical anisotropy of Mg alloy.(2) Uniaxial tensions were carried out on a rolled AT63Mg alloy plate. It was found that,the texture evolution during the tensions along rolling direction (RD) and TD resultsmainly from dislocation slip. The texture variations in (0002)poles were related tobasal slip, while those in (1010)poles were attributed to both non-basal a andnon-basal c a slips. The final textures of the two tensile samples exhibit thelowest SF values for all slip systems. This conclusion shed light on the relationship ofbetween the dislocation slip and texture evolution during uniaxial strain.(3) PSCs were applied on a rolled AT63Mg alloy plate. The twinning mode depended mianly on the compressive strain direction, meanwhile the amount and morphology oftwins varied significantly with the expensive strain direction. It was shown that thetwinning behaviors during PSCs were conducted by the twinning strain, i.e., the twinvariants with small twinning strain along constraint direction will be activatedpreferentially. This criterion is helpful for the twinning analysis during PSCs.(4) Single hard-plate rolling (SHPR) was tests were conducted on AT63Mg alloy. Owingto the addition of one hard steel plate, the cracks of the SHPRed samples wassignificantly decreased. Thus, large thickness reduction can be induced in one rollingpass, and the resulting AT63Mg alloy sheet exhibited small average grain size of4mand high tensile strength of330MPa.(5) Wave-shaped die rolling (WDR) were conducted on AT63Mg alloy. The addition ofwave-shaped die was found to modify the symmetric shear stresses during rolling,resulting in a significant weakening in the basal texture of WDRed sheets. Due to theweakened basal texture, the WDRed sheets presented strong strain hardening capacity(n=0.295) and high elongation to failure (δf=22.5%).(6) Double hard-plate rolling (DHPR) tests were conducted on AT63Mg alloy. Due to theaddition of two hard steel plates, large thickness reduction above85%can be inducedat350oC by just one pass. The DHPRed AT63Mg alloy sheets presented concurrentlyhigh tensile strength and high elongation (σb=371MPa, δf=27%). Moreover, DHPRwith large thickness reduction (85%+5%) was also suitable for AZ91Mg alloy whichhas very limited formability. The DHPRed AZ91sheet exhibited excellentstrength/ductility combination (σb=371MPa, δf=27%). DHPR is applicable to otheralloys having poor formability, and paves a way for their industrial applications.In summary, this paper investigated the deformation behaviors of extruded and rolledAT63alloys during uniaxial deformations, which presented the twinning mechanism indually basal-textured alloy and revealed the relationship between dislocation slip and textureevolution. The deformation behaviors of rolled AT63alloy during PSC were alsoinvestigated, which shed light on the twinning criterion during PSC. Additionally, innovativerolling approaches were proposed in this paper, and were found to be effective forweakening the rolling basal texture and improving the rolling efficiency of Mg alloys.