Yongyi Peng

Comparison of FSW and TIG welded joints in Al-Mg-Mn-Sc-Zr alloy plates

Abstract In order to study the welding process, microstructure and properties of Al-Mg-Mn-Sc-Zr alloy, comparative methods of friction stir welding (FSW) and tungsten inert gas (TIG) were applied to the two conditions of this alloy, namely hot rolled plate and cold rolled-annealed plate. The relationships between microstructures and properties of the welded joints were investigated by means of optical microscopy and transmission electron microscopy. Compared with the base metal, the strength of FSW and TIG welded joints decreased, and the FSW welding coefficients were higher than the TIG welding coefficients. The loss of substructure strengthening and a very little loss of precipitation strengthening of Al3(Sc, Zr) cause the decreased strength of FSW welded joint. But for the TIG welded joint, the disappearance of both the strain hardening and most precipitation strengthening effect of Al3(Sc, Zr) particles contributed to its softening. At the same time, the grains in weld nugget zone of FSW welded joints were finer than those in the molten zone of TIG welded joints.

Effect of minor Sc and Zr on superplasticity of Al-Mg-Mn alloys

Abstract The effect of Sc and Zr on the superplastic properties of Al-Mg-Mn alloy sheets was investigated by control experiment. The superplastic properties and the mechanism of superplastic deformation of the two alloys were studied by means of optical microscope, scanning electronic microscope and transmission electron microscope. The elongation to failure of Al-Mg-Mn-Sc-Zr alloy is larger than that of Al-Mg-Mn alloy at the same temperature and initial strain rate. The variation of strain rate sensitivity index is similar to that of elongation to failure. In addition, Al-Mg-Mn-Sc-Zr alloy exhibits higher strain rate superplastic property. The activation energies of the two alloys that are calculated by constitutive equation and linear regression method approach the energy of grain boundary diffusion. The addition of Sc and Zr decreases activation energy and improves the superplastic property of Al-Mg-Mn alloy. The addition of Sc and Zr refines the grain structure greatly. The main mechanism of superplastic deformation of the two alloys is grain boundary sliding accommodated by grain boundary diffusion. The fine grain structure and high density of grain boundary, benefit grain boundary sliding, and dynamic recrystallization brings new fine grain and high angle grain boundary which benefit grain boundary sliding too. Grain boundary diffusion, dislocation motion and dynamic recrystallization harmonize the grain boundary sliding during deformation.

A Series of Zr-Based Bulk Metallic Glasses with Room Temperature Plasticity

A group of plastic Zr-Al-Ni-Cu bulk metallic glasses (BMGs) with low Zr content was developed and their thermal and mechanical properties were investigated. The results show that these Zr-based BMGs have a single crystallization event for all heating rates in the studied temperature region. The glass transition temperature Tg decreases with increasing Zr content for all heating rates. There are two melting procedures for the BMGs whose Zr content is less than 52 at %, while three melting procedures for the other Zr-based BMGs. The second melting procedure is split into two melting procedures for Zr52.5Al12.2Ni12.6Cu22.7 and Zr53Al11.6Ni11.7Cu23.7 BMGs, while the first melting procedure is split into two melting procedures for the other BMGs. The activation energy decreases with increasing sensitivity index β for the studied Zr-based BMGs. The plastic strain εp is in the region of 0.2%–19.1% for these Zr-based BMGs. Both yield strength σy and fracture strength σf are smallest for Zr55Al8.9Ni7.3Cu28.8 BMG whose εp is largest among all studied Zr-based BMGs and reaches up to 19.1%. In addition, the mechanism for the large difference of the plasticity among the studied Zr-based BMGs is also discussed.

Phase formation, glass forming ability, mechanical and thermal properties of Cu50Zr50−x Al x (0⩽x⩽11.0) glass forming alloys

Phase formation, glass forming ability, mechanical and thermal properties of Cu50Zr50−xAlx (0⩽x⩽11.0) glass forming alloys were systematically investigated. The results show that Cu50Zr47Al3 alloy has the best glass forming ability (GFA), lowest fragility index (m) and highest fracture strength. There are B2 CuZr and B19′ CuZr phases for Cu50Zr50−xAlx (0⩽x⩽5.0) alloys. B2 CuZr phase disappears and two new phases (Cu10Zr7 and CuZr2) appear when 5.0<Al<8.0. Another new AlCu2Zr phase can be clearly observed when Al ⩾8.0. The glass transition temperature (Tg), the sensitivity of the Tg to the heating rate (B), the activation energy for Tg (Eg) and the m value all increase with increasing Al content. The supercooled liquid region (ΔTx) is larger for Cu50Zr50−xAlx (x⩽5.0) than for Cu50Zr50−xAlx (x>5.0). Cu50Zr50−xAlx (0⩽x⩽4.0) alloys are off-eutectic compositions while near-eutectic compositions for Cu50Zr50−xAlx (5.0⩽x⩽11.0) alloys. The Eg, Ex, and Ep decrease with increasing sensitive factor (β) for the studied Cu-based alloys characterized in the room-temperature brittleness. The dependence of the phase formation and GFA on the Al content is discussed.中文摘要本文系统地研究了Cu50Zr50−xAlx (0⩽x⩽11.0)合金的相形成、 玻璃形成能力、 热学和机械性能. 结果表明, Cu50Zr47Al3合金具有最好的玻璃形成能力、 最小的脆性参数和最高的断裂强度. Cu50Zr50−xAlx (0⩽x⩽5.0)合金由B2 CuZr和B19’ CuZr两相组成, 当5.0<Al<8.0 at.%时, B2 CuZr相消失而Cu10Zr7和CuZr2两个新相形成, 当Al⩾8.0 at.%时, 可以明显观察到另一AlCu2Zr新相. 玻璃转变温度、 玻璃转变温度对升温速度的敏感性、 玻璃转变激活能和脆性参数随Al含量的增加而增加. Cu50Zr50−xAlx (x⩽5.0)合金的过冷液相区比Cu50Zr50−xAlx (x>5.0)合金的大, Cu50Zr50−xAlx (0⩽x⩽4.0) 合金的成分偏离共晶成分, 而Cu50Zr50−xAlx (5.0⩽x⩽11.0)合金为近共晶成分. 玻璃转变激活能、 晶化激活能和晶化峰激活能随其敏感性因素的增加而降低. 所述的铜基合金都表现为室温压缩脆性. 另外, 对其相的形成和玻璃形成能力与Al含量的关系也进行了探讨.

Effects of aspect ratio and loading rate on room-temperature mechanical properties of Cu-based bulk metallic glasses

Abstract Room-temperature mechanical properties of Cu 50 Zr 40 Ti 10– x Ni x (0≤ x ≤4, mole fraction, %) bulk metallic glasses (BMG) with aspect ratios in the range of 1:1–2.5:1 and loading rates in the range of 1×10 −5 –1×10 −2 s −1 were systematically investigated by room-temperature uniaxial compression test. In the condition of an aspect ratio of 1:1, the superplasticity can be clearly observed for Cu 50 Zr 40 Ti 10 BMG when the loading rate is 1×10 −4 s −1 , while for Cu 50 Zr 40 Ti 10– x Ni x ( x =1–3, mole fraction, %) BMGs when the loading rate is 1×10 −2 s −1 . The plastic strain ( ɛ p ), yielding strength ( σ y ) and fracture strength ( σ f ) of the studied Cu-based BMGs significantly depend on the aspect ratio and the loading rate. In addition, the σ y of the studied Cu-based BMGs with an aspect ratio of 1:1 is close to the σ f of those with the other aspect ratios when the loading rate is 1×10 −2 s −1 . The mechanism for the mechanical response to the loading rate and the aspect ratio was also discussed.

Transition of plasticity and fracture mode of Zr–Al–Ni–Cu bulk metallic glasses with network structures

Abstract Effect of network structure on plasticity and fracture mode of Zr–Al–Ni–Cu bulk metallic glasses (BMGs) was investigated. The microstructures of transversal and longitudinal sections were exposed by chemical etching and observed by scanning electron microscopy (SEM). The mechanical properties were examined by room-temperature uniaxial compression test. The results show that both plasticity and fracture mode are significantly affected by the network structure and the alteration occurs when the size of the network structure reaches up to a critical value. When the cell size (dc) of the network structure is ∼s3 μm, Zr-based BMGs characterize in plasticity that decreases with increasing dc. The fracture mode gradually transforms from single 45° shear fracture to double 45° shear fracture and then cleavage fracture with increasing dc. In addition, the mechanisms of the transition of the plasticity and the fracture mode for these Zr-based BMGs are also discussed.