Wang Zhaodong

不同Mg/Si比对含Zn的Al-Mg-Si合金再结晶组织及性能的影响

为改善Al-Mg-Si系合金汽车板综合性能，通过浇铸法制备出3组合金成分铸锭，并经过均匀化、热轧、中间退火、冷轧，获得1 mm厚的合金板材.合金板材经560 ℃固溶30 min后，立即在100 ℃条件下预时效8 h，室温停放14天，模拟铝板转运存储过程，并拉伸变形2%，再在185 ℃下进行20 min烘烤处理，实现烘烤硬化.采用金相显微镜、装备电子背散射衍射的扫描电镜对合金进行显微组织观察及织构分析，通过万能电子试验机进行力学性能测定，研究不同Mg/Si比和高Zn元素对合金再结晶组织及织构、烘烤硬化性以及腐蚀敏感性的影响.结果表明，Mg/Si比相等合金再结晶组织更加均匀细小，平均晶粒尺寸190 μm，存在相对较少的Cube织构{001} 和较多的P型织构{011} ；高Mg合金、高Si合金局部晶粒粗大，Cube织构{001} 较多，P型织构{011} 较少；预时效后，Mg/Si比相等合金强度较高，且烘烤硬化性优异，烤漆硬化增量达到107 MPa；烤漆后，更多的Zn原子扩散到晶界上，强化晶界微电流反应，欠时效态Mg/Si比相等合金较高Mg合金、高Si合金抗腐蚀敏感性降低，被腐蚀深度为121 μm.

Precipitation Behavior of Nanometer‐Sized Carbides in A Nb‐Ti‐Bearing Low‐Carbon Steel

The microstructure, mechanical property and precipitation behavior in a low carbon Nb-Ti micro-alloyed steel were investigated using dilatometer, optical microscopy and transmission electron microscope. The results show that the microstructure of the experimental steel treated by isothermal quenching process mainly consists of ferrite and martensite. The volume fraction of ferrite increases with a decrease in the isothermal temperature. It is found that both of interphase precipitation and supersaturated precipitation would appear in the samples treated by isothermal quenching process. Along with the isothermal temperature decreasing, the precipitation state changes from interphase precipitation to supersaturated precipitation. The interphase precipitation of these carbides with different row spacing and different orientation in ferrite grains, is related to the mobility of interfaces during γ/α transformation based on ledge mechanism. In addition to {110}α plane suggested by the ledge mechanism, the planar sheets of interphase precipitation are also found to be parallel with{035}a planes. Moreover, the interphase precipitation carbides were identified to have a NaCl-type crystal structure with a lattice parameter of 0.432 nm and obey the Baker-Nutting (B-N) orientation relationship with respect to ferrite matrix. The contribution of the precipitation hardening to the yield strength of the experiment steel has been estimated to be ~337 MPa at 620 °C, based on Orowan mechanism.

Product Design and Production Practice of 700MPa High Strength Hot Rolled Strip for Auto Axle Tube

According to the technical specifications of 700MPa high strength automotive axle tube steel, a low cost of 0.07%C+1.5%Mn+0.05%Nb+0.10%Ti was designed. The high strength mainly relies on grain refinement strengthening and precipitation strengthening. The recrystallization, precipitation, and CCT curves of the 700MPa grade axle tube steel were studied in order to determine a reasonable TMCP process. By controlling the low level segregation band, low level of C and N content, 700MPa grade high strength automotive axle tube steel is successfully developed with excellent mechanical property, welding property, flattening and flaring property, torsion fatigue property, static torsional property and surface quality.

Camera mathematic model of the molten steel level detection in the strip casting process

A CCD system was designed to detect the molten steel level in the strip casting process. According to the image computing method, camera mathematic model of the molten steel level detection was established. Then an experiment was carried out to calibrate the model parameters and the precision of the mathematic model was tested. The result illustrates that the camera mathematic model and calibrate method of the molten steel level are feasible, which show high levels of precision and can be applied in the industrial line for the strip casting.