1、Application Background

Copper alloy is a kind of alloy with pure copper as the matrix and one or several other alloying elements. Pure copper is rose red metal, the surface of the formation of copper oxide film is purple, so industrial pure copper is often called red copper or electrolytic copper. Pure copper has excellent electrical conductivity, thermal conductivity, plasticity, ductility and corrosion resistance. Common copper alloys are divided into brass, bronze and white copper. Brass is zinc as the main element of the copper alloy, with good mechanical, physical and technological properties, has been widely used in various industrial fields. White copper, also known as copper-nickel alloy, is a copper-nickel-zinc alloy with nickel as the main addition. The color is silver white, with high strength, hardness and plasticity, good corrosion resistance and higher resistivity. It is mainly used in the manufacture of ornaments, water appliances, instruments and instruments and currency. Bronze, originally refers to copper tin alloy, later except brass, copper alloys are all called bronze, and often in the name of bronze before the first major addition element name.

The brass studied in this paper is copper alloy with zinc as main element, which is divided into ordinary brass and special brass. Ordinary brass is a binary alloy of copper and zinc. Different mechanical properties of brass can be obtained by changing the content of zinc in brass. The higher the content of zinc in brass, its strength is higher, slightly lower plasticity. The zinc content of brass used in industry is not more than 45%, and the high zinc content will produce brittleness and deteriorate the alloy performance, so the zinc content is very important to the performance of ordinary brass. In order to improve the performance of brass, on the basis of ordinary brass to add other alloy elements, three or multiple copper alloy, namely special brass, commonly used alloy elements are manganese (Mn), aluminum (Al), silicon (Si), iron (Fe), tin (Sn), lead (Pb), nickel (Ni) and so on.

(1) zinc: the role in brass is mainly to improve the strength, improve casting performance.

(2) iron: the amount of iron in brass is generally 1~3%. It can refine grain, improve strength and hardness, increase corrosion resistance, but beyond this value, make the alloy brittle, reduce plasticity and corrosion resistance.

(3) Manganese: manganese can improve the strength and hardness of brass, and increase the corrosion resistance, and do not reduce the plasticity.

(4) aluminum: a small amount of aluminum can significantly improve the strength of brass, but also reduce its plasticity. Aluminum can improve the corrosion resistance, improve the fluidity of the alloy, casting surface quality is better.

(5) Silicon: a small amount of silicon can significantly improve the strength and hardness of brass, but also significantly reduce the plasticity. Silicon also improves the corrosion resistance and casting properties of brass.

(6) Lead: mainly used to improve the cutting performance of brass.

(7) tin: tin is mainly used to improve the strength and corrosion resistance of brass, so the tin brass is also called naval copper gun. The amount of tin is generally controlled under 1%.

(8) Nickel: used to refine the structure, improve impact toughness and corrosion resistance.

2、Composition Analysis Of Brass

In the composition analysis of brass, the content of copper and zinc is the main object of concern, and other added elements are generally tin, lead, nickel, iron and manganese. At present, the composition analysis of common brass is divided into chemical analysis and spectral analysis.

3、Chemical Analysis

Chemical analysis based on chemical reactions of substances can be divided into titration analysis and gravimetric analysis according to different operating methods:

① According to the concentration and volume of the standard solution consumed by titration and the chemical reaction measurement relationship between the measured substance and the standard solution, the content of the measured substance is calculated. This analysis is called titration analysis.

② According to the chemical properties of the substance, choose the right chemical reaction, will be measured components into a fixed composition of precipitation or gas form, through passivation, drying, burning or absorption of absorbent after a series of treatment, determine the weighing, find out the content of the measured components, this analysis is called gravimetric analysis.

The national standards involved in chemical analysis are:

GB/T 5231-2012 Processed copper and copper alloy grades and chemical composition

GB/T 1176-2013 Cast copper and copper alloy

Methods for chemical analysis of copper and copper alloys

Using chemical analysis method to test the composition of brass requires a lot of chemical reagents and it is difficult to control the human error in the testing process.

4、Spectral Analysis

Since each atom has its own characteristic spectral line, it is possible to identify a substance and determine its chemical composition based on the spectrum, a method called spectral analysis. For spectral analysis, emission spectrum and absorption spectrum can be used. The advantage of this method is that it is very sensitive and fast. At present, direct reading spectrum analysis and X-ray fluorescence spectrum are mainly used for spectral analysis.

① In the direct reading spectrum analysis, the high copper content makes the direct reading spectrum can not be directly tested, only by determining all other elements to obtain the copper content of the residual amount. However, when the content of zinc is high, the measurement effect of direct reading spectrum is not ideal, resulting in the measurement accuracy of copper is not enough.

② X-ray fluorescence spectroscopy is good at the analysis of major and trace elements, which can completely meet the requirements of brass composition analysis. At present, the common X-ray fluorescence spectrum analysis includes wavelength dispersive X-ray fluorescence (WDXRF) and energy dispersive X-ray fluorescence (EDXRF). The test performance of EDXRF and EDXRF is similar, but the cost is lower, and it is easier to popularize and apply in enterprises. An EDXRF instrument (ScopeX) developed by LANScientific was used to determine the elements in brass.

5、Application Design

5.1Instrument configuration and test conditions

Instrument model: ScopeX

Serial number: 330041

X-ray tube: W target

Detector: SDD detector

Test environment: air

Test conditions: tube pressure 40 kV, tube flow 240 μA, filter Mo100, target W, TIS Beam W40Al2000, test time 60 s.

Brass 360 standard sample: LiveTime: 73.83% CPS: 40002

5.2 Standard sample content

CDA (Copper Development Association Inc) standard Copper sample and pure Al standard sample (Cu content 0 % factor) were used to make application curve. Specific standard sample parameters are shown in Table 1.

Table 1 Content table of copper alloy and pure Al standard sample

Note: Other elements in the standard sample, such As C, Al, Si, P, S, As, Sb, etc., are not listed due to their low content, which is not considered in this test

5.3Elements Selection

Considering the types and contents of elements contained in brass, the spectral lines of elements Fe and Ni to be measured will be interfered by possible element Co, so the matrix rules are selected. At the same time, the existing standard samples have standard values and are similar to the base, so the empirical coefficient method is selected to test elements including Al, Si, Mn, Fe, Co, Ni, Cu, Zn, As, Sn, Sb and Pb. The boundary of the selected elements is set, and the calculation method and strength rules are shown in Table 2.

Table 2 Element boundary, calculation method and strength rule

5.4Calibrate and calibrate the curve

Considering that the content of impurity elements (C, Al, Si, P, S, As, Sb) in the selected sample is lower than 0.02%, and the influence on the principal elements can be ignored, the normalized algorithm is selected to establish the curve for the principal elements (Cu, Zn, Pb, Sn, Fe, Ni, Mn), and the primary standard curve is used to calibrate the curve. The calibration curve obtained is as follows: