Joining Technology of Dissimilar Materials for Automotive Components(Ⅱ)

Joining techniques of dissimilar materials for lightweight multi-material automotive body structure were discussed. The joining of 1 .4 mm thickness steel and 2 mm thickness of Al were performed by the new method that is hybrid laser welding system. After aluminum and steel were welded by laser hybrid welding process, the micro-structure investment and the micro-hardness test were carried out. Hybrid laser welding promises a bright future in joining technology of dissimilar materials for automotive components.

Study of residual stresses in tailor rolled blanked Al5J32-T4 sheets

Several automotive parts such as door panels have been manufactured by using load-adapted blanks for crash optimization and weight minimization. Recently, Tailor Rolled Blanks (TRB) has been introduced to remove the disadvantages of a welding process which was used in joining panel components. TRB offers better structural design capabilities due to the seamless transitions on the panels with different thicknesses. In spite of the advantages of the process, TRB leaves internal stresses in the panel. This residual stresses lower the formability of Tailor Rolled Blanked (TRBed) parts and cause cracks near severe curvature during subsequent forming processes. In this research, the residual stresses of TRBed Al5J32-T4 sheets were studied by X-ray stress analysis, and also microstructure was observed along the rolling direction. In addition, heat treatment was done after TRB process in order to compare the residual stresses to that of the TRBed sheets before the heat treatment.

Evaluation of Alpha-case in Titanium Castings

The alpha-case formation reactions between Ti and investment molds （Al-2O-3,ZrSiO-4,ZrO-2,CaO stabilized ZrO-2） were evaluated in a plasma arc melting furnace.Regardless of thermodynamic approaches,there were distinct alpha-case formations.The reaction products were characterized by electron probe micro-analysis and transmission electron microscopy.Theα-case generation between Ti and Al-2O-3 mold was not able to be explained by the conventionalα-case formation mechanism,which is known to be formed by the interstitials,especially oxygen dissolved from mold materials.However,from our experimental results and thermodynamic calculations,it was confirmed that theα-case is formed not only by an interstitial element but also by substitutional metallic elements dissolved from mold materials.Our newly establishedα-case formation mechanism will surely lead to a variety of significant applications of theα-case controlled Ti casting.

Prediction of forming limit curve for pure titanium sheet

Commercially pure titanium（CP Ti） has been actively used in the plate heat exchanger due to its light weight, high specific strength, and excellent corrosion resistance. However, researches for the plastic deformation characteristics and press formability of the CP Ti sheet are not much in comparison with automotive steels and aluminum alloys. The mechanical properties and hardening behavior evaluated in stress-strain relation of the CP Ti sheet are clarified in relation with press formability. The flow curve denoting true stress-true strain relation for CP Ti sheet is fitted well by the Kim-Tuan hardening equation rather than Voce and Swift models. The forming limit curve（FLC） of CP Ti sheet as a criterion for press formability was experimentally evaluated by punch stretching test and analytically predicted via Hora＇s modified maximum force criterion. The predicted FLC by adopting Kim-Tuan hardening model and appropriate yield function shows good correlation with the experimental results of punch stretching test.

The Development of Thermal Conductive Polymer Composites for Heat Sink

The thermal and mechanical properties of the polyamide 6/boron nitride and polyphenylene sulfide/graphite composites have been investigated as a function of composition and size of fillers. The addition of highly thermal conductive h-BN and graphite gives rise to large increase （about 2 times） of thermal conductivity of individual polymer. In PPS/graphite system, the higher conductivity value was obtained when smaller graphites were added. Meanwhile, the tensile and flexural strength are reduced upon increasing filler loading.

Evaluation the Properties of Titanium Matrix Composites by Melting Route Synthesis

The main purpose of this study is an in-situ synthesis of （TiB＋TiC） hybrid titanium matrix composites （TMCs） by vacuum induction melting method and to verify its mechanical properties.The melting route was adopted to synthesize the commercial pure titanium （cp Ti） and granular boron carbide （B-4C）.The reinforcements,the fraction of 10 vol.pct,were formed by adding 1.88 wt pct B-4C to cp Ti.After in-situ synthesis of TMCs,electron probe micro-analysis elemental mapping was carried out to confirm the distribution and shape of reinforcements.The cone-on-disk type sliding wear test was also done for the identification of TMCs.It is concluded that （TiB＋TiC） hybrid TMCs can be in-situ synthesized and has better wear properties than H13.

Study of Dielectric and Thermal Conductivity Characteristics of Polyimide Composite

The graphene is used to enhance the thermal conductivity, but it is difficult to obtain uniform dispersion and low dielectric property. We fabricate the polyimide composite with high thermal conductivity and low dielectric property. It changes the filler contents, and examines curing time and dispersion. The dispersion characteristics were quantified by absorbance measurement. The graphene 0.1 wt% and BN 0.5 wt% polyimide composites show a thermal conductivity of 6.6 W/m®K by LFA (Laser Flash Analysis) and a dielectric constant of 4.6@10 GHz by SPDR (Split Post Dielectric Resonators).

Effect of Improving the Slip Properties of the Organic Materials on the Inorganic Filler in Heat Dissipated Pad

The heat dissipated pad is made of composite mixing silicon or epoxy resin with thermal conductive inorganic fillers. The heat-dissipation material improves performance as the amount of thermal conductivity filler increases. However, the optimum recipe should be determined by considering the price and pad formability. In this study, high performance thermal pad is made of silicon resin mixed with Al2O3 as a thermally conductive filler. Since Al2O3 is low cost, it can use much filler. Al2O3 has improved slip-ability with organic coating on it to increase the viscosity of the slurry. The same process and the same recipe, could maximize the amount of the filler. As a result, the thermal conductivity is lower by 10%. But the viscosity is reduced by 60%, too. So form-ability is getting priority.

Statistics of oxidation resistance of Ni-(0-15)Co-(8-15)Cr-(0-5)Mo-(0-10)W-(3-8)Al-(0-5)Ti-(0-10)Ta-0.1C-0.01B superalloys at 1000℃ by compositional variations

The effects of alloying elements(Co,Cr,Mo,W,Al,Ti,and Ta)on the oxidation resistance of Ni-(0-15)Co-(8-15)Cr-(0-5)Mo-(0-10)W-(3-8)Al-(0-5)Ti-(0-10)Ta-0.1 C-0.01 B alloys were studied.The sample compositions were designed by the Box-Behnken method of design of experiments(DOE).The alloying elements show complicated effects on the mass gain due to oxidation,depending on the alloy composition.Al reduces the mass gain largely.The other elements except Al do not appear to exert a strong effect on the oxidation rate on average,but their influences are shown clearly in the alloys with a low Al content.Co,W,and Ta reduce the oxidation rate,while Cr,Mo,and Ti promote oxidation.Ta is the most effective element in reducing the oxidation rate of the alloy with a low Al concentration.It is confirmed that a continuous Al2O3 layer is essentially required for high oxidation resistance.The oxide scale of easily oxidized alloys has various oxides such as NiCr2O4,NiAl2O4,NiO,Cr2O3,CrTaO4,and TiO2.

Mechanical properties and flame retardancy of surface modified magnesium oxysulfate(5Mg(OH)_(2)·MgSO_(4)·3H_(2)O)whisker for polypropylene composites

Magnesium oxysulfate(MOS)whisker is considered as a promising inorganic material recently attracting a great attention for being used as a reinforcing filler for polymer composites due to high aspect ratio and extremely-low bulk density.In this study,the MOS was treated with 3-methacryloyloxypropyl-trimethoxy silane(MPS)via sol-gel condensation reactions,which successfully allowed melt mixing with polypropylene(PP)up to 30 wt%of MOS.The tensile strength at yield and modulus of the MOS/PP composites were substantially increased by 50.8%and 362%,respectively,when compared with the pristine PP.As a novel finding,the flame retardancy of MOS was proved by identifying water evolution at elevated temperatures giving out 9 wt%of water in 250-320℃and 14 wt%in 350-420℃in two steps.This work demonstrated that the MOS could be an excellent filler for PP not only increasing the mechanical properties in a great extent but also imposing flame retarding capability.