To reveal the effect of Zn element on the microstructure and mechanical properties of Mg-Bi-Sn alloy, Mg-3Bi-5Sn-xZn (x=0, 1, 2, 3, wt%) alloys were prepared by casting. Using OM, SEM, XRD, EPMA, Vickers hardness tester and tensile testing machine, the effect of Zn element on the microstructure and mechanical properties of Mg-3Bi-5Sn (BT35) alloy was studied. The experimental results show that Zn element can significantly reduce the grain sizes of BT35 alloy. With the increase in Zn content, the grain size of BT35 alloys decreases significantly at first and then increases slightly, among which Mg-3Bi-5Sn-2Zn (BTZ352) alloy has the smallest grain size (58.2 mu m). In addition, there are two kinds of second phases, Mg3Bi2 and Mg2Sn, observed in BT35 alloys, and additional Mg2Zn phase and BiSn phase can be detected in the microstructure after adding Zn element. When the addition of Zn element is less than 3wt%, the tensile strength and elongation of the alloy firstly increase and then decrease slightly. Among them, BTZ352 alloy shows the best mechanical properties with the tensile strength and elongation of 263.5 +/- 6.0 MPa and 13.2%+/- 0.6%, respectively; and the fracture microstructure of BTZ352 alloy exhibits typical transgranular fracture characteristics.
Alloying is one of the main methods to improve the performance of Cu-Ti alloys,and it is expected to obtain high performance to replace Cu-Be alloys.A Cu-4Ti-0.5Cr-1Mg alloy was designed,and the effects of thermomechanical treatment on the microstructure and properties of the alloy were investigated.Optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffractometry(XRD)were used to analyze the microstructure and phase constituents,and the mechanical properties and electrical conductivity of the material were determined as well.The results show that the addition of Cr and Mg alloy elements does not change the aging sequence of Cu-Ti alloy,but lead to the formation of Cr2Ti intermetallic compounds,and precipitation of β-Cu4Ti phase is inhibited with the increase of the aging time.After 40%cold rolling and 380℃aged for 1 h,the alloy can acquire excellent comprehensive properties,the hardness and strength are 350HV and 1220 MPa,respectively,and the conductivity is 10.84%IACS.The ultra-high strength of design alloys is mainly attributed to β'-Cu4Ti dispersion precipitation strengthening and work hardening.
In this study, the ambient temperature fretting wear behavior and the wear mechanisms of the Selective Laser Melting prepared IN738LC alloy with various micro-structures were systematically investigated under varying load conditions (35N, 100N). The results indicate that the running states of fretting gradually transitions from the gross slip regime (GSR) to the mixed slip regime (MSR) as the load increases. The HT-2 samples (Unimodal precipitation, hardness 512 HV) present more fine homogeneous and dense secondary γ′ phase compared with HT-1 (Bimodal precipitation, hardness 487 HV) and As-built (No precipitation, hardness 392 HV) counterpart, which result in excellent wear resistance. The main fretting wear mechanisms for all samples were oxidation wear, abrasive wear, fatigue wear.
采用熔铸法制备了不同Cu和Li含量,Cu、Li质量比及Sc、Ti元素添加的铝锂合金,通过金相组织观察、阳极覆膜金相观察、DSC测试、扫描电镜(SEM)观察、EDS元素分析等研究Cu、Li含量及Sc、Ti元素添加对铝锂合金均匀化优化工艺规律的影响.结果表明:铸态合金中存在粗大Al2Cu相,含Ag、Zr(Sc)的晶界Al-Cu相和晶界AlCuMnFe(Ti)难熔相三种成分粒子;铝锂合金中优选均匀化温度随着Cu含量的升高而提高,并随着Cu、Li质量比的升高而降低;Sc元素的添加有利于优选均匀化温度的降低;Sc、Ti元素的复合添加促进优选均匀化温度的提高.
电子束选区熔化增材制造是金属增材制造领域的重要发展方向.为了理解和控制电子束扫描过程中熔池流场与温度场演化规律,并进一步探明和预测凝固成形件的微观组织形成过程,提高零件的冶金质量和力学性能,本文采用基于格子玻尔兹曼方法及有限体积法混合格式的三维传热传质模型,对熔池的形貌尺寸、温度场、流场及相场演化进行模拟.结果表明,当电子束扫描速度从800 mm/s增加到1600 mm/s时,冷却速度从0.19 K/μs增加到0.45 K/μs,温度梯度从0.99 K/μm增加到3.72 K/μm.进一步采用基于格子玻尔兹曼方法的微观枝晶生长模型探究微观组织形成机制,研究发现,固液界面处出现沿温度梯度方向生长的柱状晶,且电子束扫描速度越大,柱状晶生长越快,熔体流动可在一定程度上促进柱状晶的生长.
