Research On The Obdurability Aluminum Alloys For Diesel-engine Cylinder Head Applications

Weight reduction in vehicles has important benefits of fuel economy and reductionin greenhouse gas emissions as well as improved vehicle performance. The currentmaterial for the diesel-engine cylinder head is mostly cast iron and replacing it withaluminum alloys would result in very effective weight reduction. In order to adapt to theincrease of the engine power, the research attempts to improve the microstructure ofaluminum alloys, which is used in diesel-engine cylinder head, and to enhance itsproperties by adding trace element. In this paper, the effect of Sr, RE and Mg on themicrostructure and properties of ZL114A alloys were systematically investigated, byanalyzing microstructure and mechanical properties testing of the alloys. On the basis,the better process scheme is proposed through the optimization of process parameters.The influence of Sr modification on the microstructure and properties of theZL114A alloys were systematically investigated. The results show that the addition ofSr content can reduce the size of eutectic Si particles and improve the mechanicalproperties of ZL114A alloys. The alloys can be fully modified by0.03wt%Sr additionand obtain the excellent properties after T6heat treatment whose tensile strength, yieldstrength and elongation reach316.5MPa,259.3MPa and4.7%respectively and canmeet the material requirements of diesel engine cylinder head. Much more addition ofSr content causes the coarser of eutectic Si particle, the defections of shrinkage porosityand cavity etc, which weaken the tensile properties of the alloys. After the Sr additionand T6heat treatment, a lot of small and deep dimples are observed from the fracturemorphology, which enhances the ductility of alloys and makes its fracture mechanismstransform from brittle fracture to ductile fracture.The influence of RE element on the microstructure and properties of the ZL114Aalloys were systematically investigated. The results show that the addition of REcontent can reduce the size of eutectic Si particles and primary phase-Al. When the amount of RE addition reaches0.2%, the-Al and eutectic Si present the smallestrespectively. But, much more addition of RE content causes the coarser of the-Al andeutectic Si. With the increase of RE content, the tensile properties of the alloys begin toascend and then come down, the best was reached by0.2%RE addition. The REmodification can make the fracture mechanisms of alloys transform from brittle fractureto ductile fracture.On the basis of0.2%RE addition, the Mg enhancement was studied. With theincrease content of Mg addition, the tensile strength, yield strength and hardness valueof ZL114A alloys increases, but the elongation decrease. The change law abovebecomes more obviously after T6heat treatment. The ZL114A alloys can obtain highintensity as well as good ductility with adding0.1%Mg and0.2%RE into it, whosetensile strength, yield strength, elongation and hardness reach349.1MPa,312.2MPa,3.89%and102HBS after T6heat treatment and can meet the material requirements ofdiesel engine cylinder head.