Mechanical Engineering Materials and Mechanics How do you re

Mechanical Engineering (Materials and Mechanics)

How do you read hardness values?

For example: Al-7075 HRB , Al-6061-T6 HRB and St-AISI-1018 HRB

I know that\'s the Rockwell Hardness B-scale but are the 4 digits just identification for the Aluminum and steel materials or do they represent something else? Apparently the \'T6\' portion is the treatment method, I\'m not too clear on that.

Please be detailed in the response. Thank you.

Solution

Hardness values have different representation according to different test like rockwell , vickers, BHN etc

let us take Rockwell B scale in this situvation

First session represents the parent material and its alloy

Al-7075 represents aluminium alloy with 5.6-6.1%of zinc as primary alloying element

Al-6061 T6 represents aluminium alloy with silicon and manganese as mojor alloying element

St- AISI -1018 is low carbon steel having 0.6-0.9 % manganese

T6 is the heat treatment normally in aluminium alloys are heat treated by using precipitation hardening it countain two steps , heating in a molten pool and artifical aging . on heating upto solution form helps to dissolve all the alloying elements in solid solution then quenching in water quickly ,this cooling prevent the alloying elements from precipitation . thus we have a solid solution if Si,Mn and other elements in aluminium at room temperature

this is T4 temper , if we take this material and heat treat its temperature between 325-400 deg F the alloying elements began toform ordered array of atoms in Al structure this strengthened the Al this is called aging which results with a T6 temper , three commonly used time/temp ycle for aging - 1 hr at 400 degF, 5hr at 350degF, 8 hr at 325degF all are equally effective

HRB represents Rockwell hardness B scale , hardness is calculated by HR= N-d/s were d is the depth, N and s are scale factors, In HRB load is 100kgf and the size of indenter is 1/16 inch dia steel sphere . This scale is mainly used in Aluminium, brass and soft steel its N value is 100 and s= 0.002mm

Like HRB other scales are differ in their load value and size/type of indenter used