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Recently, it has been expected that titanium alloy valves will be adopted at extremely high rate to motorcycle engines where higher engine performance is required than in automobiles. However, there were difficulties with respect to reliability required for motorcycle engines. The reason for this is that engine valves of motorcycle engines are not only smaller in stem diameter, but also used at a higher maximum engine speed than those of automobile engines. This study is about a development of titanium alloy engine valves that meet reliability requirements in motorcycle engines.

To give the wear-resistance to titanium intake valves by simple oxidation treatment, oxidation condition and microstructure of Ti-6Al-4V bars were studied. The wear test using a valve simulator shows that the wear of the face oxidized at 820°C for 1 and 4h in air is superior to that of ferrous valves. The best micro-structure of Ti-6Al-4V bar is an acicular structure with the prior β grain size of 30 to 60 μ m in average, which prevents distortion during the oxidation treatment and has excellent mechanical properties.

Improvement of material characteristic values, adjustment of forming conditions as well as introduction of new forming technics are necessary to promote wide application of aluminum alloy sheets into automotive parts. 5000 series and 6000 series aluminum alloy sheets are concerned about the relationship between material characteristic values and fundamental forming ability required to apply them to automobile body parts as well as the effect of lubricant on their formability. The hardening parameters, n values, of them are larger than those of cold-rolled steel sheets. However, the r values and the local elongations are extremely small. The improvement of stretch formability owing to increase of n value is smaller than that of the steel sheets. Inferior deep drawability of the aluminum alloy sheets is due to low fracture resistance force caused by low r value.

Aluminum alloy sheets are used for automotive body-panels, but their small Young's modulus results in inferior shape-fixability than conventionally-applied steel sheets with similar strengths. Smaller radius of curvature, indicating better shape-fixability, is found at the center of a panel press-formed with higher blank holder force (BHF). Higher force can be applied for press-forming of alloy sheets with larger strain-hardening exponent (n value) induced by an increased addition of Mg. Recently-developed 5000 series alloy sheets containing 5.5 pct Mg and 0.3 pct Cu have an elongation over 33 pct at an ultimate tensile strength of 270 MPa and can be press-formed with better shape-fixability.

The newly developed sheet steel lightly coated with an organic composite is as follows. Zn-Ni alloy plated sheet steel with a coating weight of 30 g/m2 and average Ni concentration of 11.5 ∼12.0 % is chromated through electrolysis. The coating weight of chromate film is 50 ∼90 mg/m2 in Cr. Furthermore, emulsified olefin-acrylic acid copolymer resin mixed with colloidal silica of particle size 7 ∼8 nm applied to a thickness of 1.0 ∼1.8 μm. Olefin-acrylic acid copolymer resin and colloidal silica are mixed at the rate of 100 and 30 (parts by weight). It maintains excellent corrosion resistance even after forming, C-ED paint corrosion resistance and paint adhesion. Furthermore, it has excellent perforation resistance. The product has excellent weldability and is well suited to continuous forming, too.

We have taken notice of Zn-Fe alloy electroplating with an eye to developing new corrosion-resistant steel sheets for automotive use with both cosmetic corrosion resistance and perforating corrosion resistance, and as a result of investigations into its paintability and corrosion resistance over the whole range of its compositions, we have come to a conclusion that steel sheets with two-layer Zn-Fe alloy electroplating that consists of a thin upper layer with a 75 to 85% Fe content and a lower layer with a 10 to 20% Fe content is the best choice.