The microstructure evolution of Mg100-2xYxZnx （x=2, 2.5, 3, 3.5） alloys was investigated. Results show that the Mg100-2xYxZnx alloys are composed of a-Mg, long period stacking ordered （LPSO） phase and eutectic structure phase （W phase）, and the Mg95Y2.5Zn2.5 alloy has the best comprehensive mechanical properties. Subsequently, the microstructure evolution of the optimized alloy Mg95Y2.5Zn2.5 during solidification and heat treatment processes was analyzed and discussed by means of OM, SEM, TEM, XRD and DTA. After heat treatment, the lamellar phase 14H-LPSO precipitated in a-Mg and W phase transforms into particle phase （MgyZn2）. Due to the compound reinforcement effect of the particle phase and LPSO phase （18R＋14H）, the mechanical properties of the alloy are enhanced. The tensile strength and elongation of the Mg95Y2.5Zn2.5 alloy is improved by 9.1% and 31.3% to 215 MPa and 10.5%, respectively, after solid-solution treatment.
Shou-zhong WuJin-shan ZhangChun-xiang XuKai-bo NieXiao-feng NiuZhi-yong You
Alloys with composition of Mg_(96-x)Gd_3Zn_1Li_x(at.%)(x=0, 2, 4, and 6) were prepared by conventional casting. The microstructures of these alloys under as-cast and solid-solution conditions have been observed, and the mechanical properties were investigated. The results showed that Li is an effective element to refine the grains and break the eutectic networks in as-cast MgGd_3Zn_1 alloy. During solid solution treatment, these broken eutectic networks are spheroidized and highly dispersed. In addition, plentiful lamellar long period stacking ordered(LPSO) phases are precipitated in an α-Mg matrix when the Li addition is not more than 4%. Solid-solution treated Mg_(92)Gd_3Zn_1Li_4 alloy exhibits an optimal ultimate tensile strength(UTS) of 226 MPa and elongation of 5.8%. The strength of MgGd_3Zn_1 alloy is improved significantly, meanwhile, the toughness is apparently increased.
Li-yun WeiJin-shan ZhangWei LiuChun-xiang XuZhi-yong YouKai-bo Nie
Mg97−xZn1Y2Alx alloys with long-period stacking ordered(LPSO)structures were prepared by conventional casting method.The optical microscopy(OM),X-ray diffraction(XRD)and the scanning electron microscope(SEM)equipped with energy dispersive X-ray spectroscopy(EDS)were used to analyze the microstructure of the alloys with different compositions.Immersion test and electrochemical measurement were used to evaluate the corrosion behavior of the alloys at room temperature,and the corrosive medium is 3.5%NaCl aqueous solution.The results showed that,with the increasing aluminum(Al)addition,exceptα-Mg and LPSO phases,new phases also emerged on the grain boundaries.At the same time,the zigzag part of LPSO phases disappeared,and the boundaries between LPSO phases andα-Mg became smooth.Furthermore,the addition of Al to Mg-Zn-Y alloys could hinder the activity of cathodic hydrogen evolution reaction and improve the uniformity and compactness of the protective surface film,thus,enhanced the corrosion resistance of Mg-Zn-Y alloys.
Dan WangJinshan ZhangJidong XuZilong ZhaoWeili ChengChunxiang Xu
To obtain a higher microstructural refining efficiency, and improve the properties and processing ability of hypereutectic AI-25Si alloy, a new environmentally friendly AI-20.6Mn-12Ti-0.9P-6.1Cu （by wt.%） master alloy was fabricated; and its modification and strengthening mechanisms on the AI-25Si alloy were studied. The mechanical properties of the unmodified, modified and heat treated alloys were investigated. Results show that the optimal addition amount of the AI-20.6Mn-12Ti-0.9P-6.1Cu master alloy is 4wt.%. In this case, primary Si and eutectic Si as well as e-AI phase were clearly refined, and this refining effect shows an excellent long residual action as it can be heat-retained for at least 5 h. After being T6 heat treated, the morphology of primary and eutectic Si in the AI-25Si alloys with the addition of 4wt.% AI-20.6Mn-12Ti- 0.9P-6.1Cu alloy changes into particles and short rods. The average grain size of the primary and eutectic Si decreases from 250 IJm （unmodified） to 13.83 pm and 35 IJm （unmodified） to 7 tim; the e-Al becomes obviously finer and the distribution of Si phases tends to be uniform and dispersed. Meanwhile, the tensile properties are improved obviously; the tensile strengths at room temperature and 300 ℃ reach 241 MPa and 127 MPa, increased by 153.7% and 67.1%, respectively. In addition, the tensile fracture mechanism changes from brittle fracture for the alloy without modification to ductile fracture after modification. Modifying the morphology of Si phase and strengthening the matrix can effectively block the initiation and propagation of cracks, thus improving the strength of the hypereutectic AI-25Si alloy.
