| High power density diesel engine has attracted more and more attention from the international academic and industrial field of internal combustion engine because of its advantages of high detonation pressure,high power,light weight and small volume,it has become the mainstream and development trend of advanced diesel engine in recent 20 years.However,compared with ordinary diesel engine,high power density diesel engine has very severe service conditions,which requires high mechanical and thermophysical properties and formability of materials used for its main components.The cylinder head is one of the most important parts of the combustion chamber of high power density diesel engine,the cylinder head bears high thermo mechanical coupling alternating load and high-speed cyclic impact load during the service period,the traditional aluminum alloy and cast iron alloy can not meet the requirements.Therefore,it is of great significance for the development of high power density diesel engine to research and develop a new type of cylinder head alloy with low density,high strength and heat resistance.Fe-xMn-yAl-8Ni-C alloy was prepared by vacuum are melting with low density and high strength heat-resistant Fe-Mn-Al system alloy as the object in this study,the influence of different contents of Mn and Al on the structure and properties of the alloy was studied.The phase,microstructure,physical and mechanical properties of the materials were tested and analyzed by XRD,SEM,EDS,TEM and other instruments.The main results and conclusions are as follows:The Fe-xMn-14Al-8Ni-C alloy mainly contains austenite phase,NiAl intcrmctallic compound and k-carbide phase.With the increase of Mn content,the content of austenite increases,the content of NiAl intcrmetallic compound decreases,and the content of k-carbide phase precipitated at the inteface between austenite and NiAl intermetallic compound and in austenite,the density and Rockwell hardness of Fe-xMn-14Al-8Ni-Calloy decrease gradually,when the Mn content is 25%,the density of the alloy reaches a smaller value of 6.41 g/cm3 and the hardness reaches a smaller value of 43.44 HRC.With the increase of Mn content,the compression ratio and compressive strength of the alloy increase gradually,when the Mn content is 25%,the compression ratio of the alloy is 42.9%and the compressive strength is 2921.6 MPa.In the composition of Fe-25Mn-xAl-8Ni-C alloy,when the A1 content increases from 5%to 18%,the austenite content in the alloy decreases gradually,and the NiAl intermetallic compound increases gradually.When the Al content is 14%,k-carbide phase precipitates at the interface between austenite and NiAl phase and inside austenite.The physical and mechanical properties show that with the increase of Al content,the density of the alloy decreases and the hardness increases gradually.When the Al content is 18%,the density reaches a smaller value of 6.26 g/cm3 and the hardness reaches a larger value of 44.06 HRC.The compressive yield strength of the alloy increases with the increase of Al content,when the Al content is 18%,the yield strength of the alloy reaches 1144.4 MPa.When the content of Al is 10%,11%,12%and 13%,the austenite deforms first in the process of in-situ tension,which makes the cracks mainly originate at the interface between austenite and NiAl intermetallic compound,and propagate along the interface,finally leading to alloy fracture.The results show that the oxidation resistance of the alloy increases with the increase of Mn content when the content of Al is fixed,and the oxidation resistance of the alloy with 14%Al content is 59.7%higher than that of the alloy with 9%Al content when the content of Mn is 25%.Through the oxidation cross section,it is observed that the oxide film is divided into two layers due to different thermal stress and thermal expansion coefficient,the outer oxide is Fe2O3 and a small amount of Mn2O3,and the inner oxide is mainly Al2O3,Mn2O3 and NiO. |
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