Research On Deformation And Heat Treatment Process Of Spray Formed High Silicon Wear-resistant Aluminum Alloy

In the context of energy saving,emission reduction and structural weight reduction,high-Si aluminum alloys have great application potential in the automotive and aerospace fields due to their excellent wear resistance,low density and low coefficient of thermal expansion.The spray-formed hypereutectic Al-Si-based multi-element alloy can obtain the spheroidized and dispersed primary Si phase without modification treatment.The ingot also has outstanding advantages such as uniform composition and fine crystal grains.Therefore,studying the evolution of microstructure and properties of spray-formed hypereutectic Al Si-based multi-element alloys during hot working has important theoretical and application value.In current dissertation,the hot deformation behavior,solid solution behavior and aging behavior of the spray-formed Al25Si4Cu1Mg(wt.%)alloy were studied by OM,SEM,EBSD,TEM,DSC,hardness,thermal expansion,friction and wear experiments.The friction and wear mechanism at both room and high temperature were also analyzes.The main conclusions are as follows:(1)The primary phases of spray-formed Al25Si4Cu1Mg(wt.%)alloys include nearly spherical primary Si phase with micron-level,Al2Cu phase and Al Cu Si Mg quaternary phase resulting from divorced eutectics.Based on the thermal compression experiment,the thermal deformation activation energy of 194.8k J/mol is obtained.The constitutive equation and thermal processing diagram of the alloy are established.The optimized thermal deformation process parameter range is:the deformation temperature is 400??450?,and the strain rate cannot exceed 1 s^-1.(2)The dynamic recrystallization nucleation mechanism of spray-formed Al25Si4Cu1Mg(wt.%)alloy is the"particle stimulated nucleation"(PSN)mechanism.The accumulation of dislocations in the front of the high-density primary phase(mainly Si phase)leads to complete dynamic recrystallization even at a lower deformation temperature(such as350°C),so the grains are further refined.(3)The spherical Al2Cu phase produced by the divorced eutectic is the most important resolving phase in the solid solution process.The divorced eutectic structure remelted when solid-solved at the temperature higher than 515?,and formed a lamellar eutectic structure again after quenching.The primary Si phase and?-Al grains coarsened with the increase of solid solution temperature and the extension of the holding time.The optimized single-stage solid solution technology is:515?,2h.(4)The precipitation sequence of spray-formed Al25Si4Cu1Mg(wt.%)alloy is:Supersaturated solid solution-GP zone-?'phase+Q'phase-?'phase+Q'phase-?phase+Q'phase-?phase+Q phase.The peak aging system of the alloy is 185?,2h.The peak-aged hardness can reach 90.1HRB,and the main strengthening phases of the peak-aged state are needle-like??phase and lath-like Q?phase.(5)The room temperature wear mechanism of spray-formed Al25Si4Cu1Mg(wt.%)alloy is mainly adhesive wear,abrasive wear and fatigue wear.It also exhibits relatively severe oxidative wear at high temperatures.After 2h peak aging at 185?,the dispersion and precipitation of??and Q?phases improve the hardness and wear resistance of the matrix.