หลังจากบดแล้ว, ชิ้นงานโลหะจะต้องได้รับการขัดเงาเพื่อขจัดรอยขูดขีดและชั้นการเสียรูปที่เกิดจากกระบวนการเจียรบนชิ้นงานทดสอบ, จนกลายเป็นกระจกเรียบๆ. ในปัจจุบัน, วิธีการขัดตัวอย่างรวมถึงการขัดแบบเชิงกล, การขัดด้วยไฟฟ้า, การขัดด้วยสารเคมีและการขัดแบบคอมโพสิต.

1.การขัดเงาแบบกลไก: ขัดด้วยเครื่องขัดพิเศษ. การขัดเงาด้วยกลไกส่วนใหญ่แบ่งออกเป็นสองขั้นตอน: ขัดหยาบและขัดละเอียด.
การขัดหยาบ: จุดประสงค์คือการเอาชั้นที่ขัดเงาออก.
ในอดีตที่ผ่านมา, the commonly used abrasive is α-Al2O3, Cr2O3 or Fe2O3 with a particle size of 10-20μm, and is used as a suspension with water. ในปัจจุบัน, artificial diamond abrasives have gradually replaced abrasive materials such as alumina, because it has the following advantages:
1) Compared with alumina, the polishing rate of diamond abrasive particles with much smaller particle size is much larger, such as the polishing rate of 4-8μm diamond abrasive particles is similar to the polishing rate of 10-20μm alumina or silicon carbide;
2) Shallow surface deformation layer;
3) Good polishing quality.
Fine throwing: also known as final throwing, the purpose is to remove the deformation layer generated by rough throwing, so that the polishing damage is reduced to a minimum. The commonly used polishing abrasives are MgO and γ-Al2O3, of which MgO has a good polishing effect, but the polishing efficiency is low and difficult to master; The polishing rate of γ-Al2O3 is high and easy to master.

2.Electrolytic polishing: The use of anodic corrosion method to make the surface of the sample smooth and bright polishing method.
Electrolytic polishing with stainless steel as the cathode, the polished sample as the anode, the container contains electrolyte, when the current is switched on, the metal ions of the sample dissolve in the solution, under certain electrolytic conditions, the sample surface of the slightly convex part of the dissolution faster than the concave, so that the sample surface is gradually rough and flat bright.
ข้อดีและข้อเสีย:
1: Compared with mechanical polishing, electrolytic polishing is a pure electrochemical dissolution process, without mechanical force, and does not cause surface deformation of the metal.
2: This method should be used for single-phase alloys with low hardness and aluminum alloy, magnesium alloy, โลหะผสมทองแดง, titanium alloy, สแตนเลส, ฯลฯ, which are difficult to do in general mechanical polishing.
3: Electrolytic polishing on the sample polishing degree requirements are low (generally with 800 water sandpaper can be ground), ความเร็วที่รวดเร็ว, ประสิทธิภาพสูง.
4: Electrolytic polishing is particularly sensitive to the non-uniformity of the chemical composition of the material and micro-segregation, and the non-metallic inclusions will be severely corroded, so it is not suitable for metal materials with serious segregation and metallographic samples for inclusion testing.
บันทึก: electrolytic polishing must choose the right voltage, control the current density, too low and too high voltage can not achieve the purpose of normal polishing.

3.Chemical polishing: The use of chemical dissolution to obtain a smooth polished surface.
The sample is dipped in a chemical polishing liquid, stirred appropriately or rubbed with cotton, and a bright surface can be obtained after a period of time. Chemical polishing has the effect of chemical corrosion, can show the metallographic structure, and can be observed directly under the microscope after polishing.
Chemical polishing is simple to operate, ราคาถูก, does not require special equipment, the original sample surface finish requirements are not high.
The composition of chemical polishing fluid varies with the polishing material. Generally mixed acid. Commonly used acids are: orthophosphoric acid, chromic acid, sulfuric acid, กรดน้ำส้ม, nitric acid and hydrogen acid; In order to increase the activity of the metal surface to facilitate the chemical polishing, a certain amount of hydrogen peroxide is added. After the chemical polishing liquid is used, the metal ions in the solution increase, the polishing effect is weakened, and it needs to be replaced frequently.